diff --git a/exercises/practice/acronym/libs/exercism/test b/exercises/practice/acronym/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/acronym/libs/exercism/test
+++ b/exercises/practice/acronym/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/affine-cipher/libs/exercism/test b/exercises/practice/affine-cipher/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/affine-cipher/libs/exercism/test
+++ b/exercises/practice/affine-cipher/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/all-your-base/libs/exercism/test b/exercises/practice/all-your-base/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/all-your-base/libs/exercism/test
+++ b/exercises/practice/all-your-base/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/allergies/libs/exercism/test b/exercises/practice/allergies/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/allergies/libs/exercism/test
+++ b/exercises/practice/allergies/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/anagram/libs/exercism/test b/exercises/practice/anagram/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/anagram/libs/exercism/test
+++ b/exercises/practice/anagram/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/armstrong-numbers/libs/exercism/test b/exercises/practice/armstrong-numbers/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/armstrong-numbers/libs/exercism/test
+++ b/exercises/practice/armstrong-numbers/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/atbash-cipher/libs/exercism/test b/exercises/practice/atbash-cipher/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/atbash-cipher/libs/exercism/test
+++ b/exercises/practice/atbash-cipher/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/binary-search/libs/exercism/test b/exercises/practice/binary-search/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/binary-search/libs/exercism/test
+++ b/exercises/practice/binary-search/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/bob/libs/exercism/test b/exercises/practice/bob/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/bob/libs/exercism/test
+++ b/exercises/practice/bob/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/circular-buffer/libs/exercism/test b/exercises/practice/circular-buffer/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/circular-buffer/libs/exercism/test
+++ b/exercises/practice/circular-buffer/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/collatz-conjecture/libs/exercism/test b/exercises/practice/collatz-conjecture/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/collatz-conjecture/libs/exercism/test
+++ b/exercises/practice/collatz-conjecture/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/darts/libs/exercism/test b/exercises/practice/darts/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/darts/libs/exercism/test
+++ b/exercises/practice/darts/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/diamond/libs/exercism/test b/exercises/practice/diamond/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/diamond/libs/exercism/test
+++ b/exercises/practice/diamond/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/difference-of-squares/libs/exercism/test b/exercises/practice/difference-of-squares/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/difference-of-squares/libs/exercism/test
+++ b/exercises/practice/difference-of-squares/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/dnd-character/libs/exercism/test b/exercises/practice/dnd-character/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/dnd-character/libs/exercism/test
+++ b/exercises/practice/dnd-character/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/eliuds-eggs/libs/exercism/test b/exercises/practice/eliuds-eggs/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/eliuds-eggs/libs/exercism/test
+++ b/exercises/practice/eliuds-eggs/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/etl/libs/exercism/test b/exercises/practice/etl/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/etl/libs/exercism/test
+++ b/exercises/practice/etl/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/flatten-array/libs/exercism/test b/exercises/practice/flatten-array/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/flatten-array/libs/exercism/test
+++ b/exercises/practice/flatten-array/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/food-chain/libs/exercism/test b/exercises/practice/food-chain/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/food-chain/libs/exercism/test
+++ b/exercises/practice/food-chain/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/gigasecond/libs/exercism/test b/exercises/practice/gigasecond/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/gigasecond/libs/exercism/test
+++ b/exercises/practice/gigasecond/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/grains/libs/exercism/test b/exercises/practice/grains/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/grains/libs/exercism/test
+++ b/exercises/practice/grains/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/hamming/libs/exercism/test b/exercises/practice/hamming/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/hamming/libs/exercism/test
+++ b/exercises/practice/hamming/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/hello-world/libs/exercism/test b/exercises/practice/hello-world/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/hello-world/libs/exercism/test
+++ b/exercises/practice/hello-world/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/high-scores/libs/exercism/test b/exercises/practice/high-scores/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/high-scores/libs/exercism/test
+++ b/exercises/practice/high-scores/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/house/libs/exercism/test b/exercises/practice/house/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/house/libs/exercism/test
+++ b/exercises/practice/house/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/isbn-verifier/libs/exercism/test b/exercises/practice/isbn-verifier/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/isbn-verifier/libs/exercism/test
+++ b/exercises/practice/isbn-verifier/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/isogram/libs/exercism/test b/exercises/practice/isogram/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/isogram/libs/exercism/test
+++ b/exercises/practice/isogram/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/kindergarten-garden/libs/exercism/test b/exercises/practice/kindergarten-garden/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/kindergarten-garden/libs/exercism/test
+++ b/exercises/practice/kindergarten-garden/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/knapsack/libs/exercism/test b/exercises/practice/knapsack/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/knapsack/libs/exercism/test
+++ b/exercises/practice/knapsack/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/largest-series-product/libs/exercism/test b/exercises/practice/largest-series-product/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/largest-series-product/libs/exercism/test
+++ b/exercises/practice/largest-series-product/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/leap/libs/exercism/test b/exercises/practice/leap/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/leap/libs/exercism/test
+++ b/exercises/practice/leap/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/list-ops/libs/exercism/test b/exercises/practice/list-ops/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/list-ops/libs/exercism/test
+++ b/exercises/practice/list-ops/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/luhn/libs/exercism/test b/exercises/practice/luhn/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/luhn/libs/exercism/test
+++ b/exercises/practice/luhn/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/matching-brackets/libs/exercism/test b/exercises/practice/matching-brackets/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/matching-brackets/libs/exercism/test
+++ b/exercises/practice/matching-brackets/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/matrix/libs/exercism/test b/exercises/practice/matrix/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/matrix/libs/exercism/test
+++ b/exercises/practice/matrix/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/meetup/libs/exercism/test b/exercises/practice/meetup/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/meetup/libs/exercism/test
+++ b/exercises/practice/meetup/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/nucleotide-count/libs/exercism/test b/exercises/practice/nucleotide-count/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/nucleotide-count/libs/exercism/test
+++ b/exercises/practice/nucleotide-count/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/pangram/libs/exercism/test b/exercises/practice/pangram/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/pangram/libs/exercism/test
+++ b/exercises/practice/pangram/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/parallel-letter-frequency/libs/exercism/test b/exercises/practice/parallel-letter-frequency/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/parallel-letter-frequency/libs/exercism/test
+++ b/exercises/practice/parallel-letter-frequency/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/pascals-triangle/libs/exercism/test b/exercises/practice/pascals-triangle/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/pascals-triangle/libs/exercism/test
+++ b/exercises/practice/pascals-triangle/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/perfect-numbers/libs/exercism/test b/exercises/practice/perfect-numbers/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/perfect-numbers/libs/exercism/test
+++ b/exercises/practice/perfect-numbers/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/phone-number/libs/exercism/test b/exercises/practice/phone-number/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/phone-number/libs/exercism/test
+++ b/exercises/practice/phone-number/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/prime-factors/libs/exercism/test b/exercises/practice/prime-factors/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/prime-factors/libs/exercism/test
+++ b/exercises/practice/prime-factors/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/protein-translation/libs/exercism/test b/exercises/practice/protein-translation/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/protein-translation/libs/exercism/test
+++ b/exercises/practice/protein-translation/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/proverb/libs/exercism/test b/exercises/practice/proverb/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/proverb/libs/exercism/test
+++ b/exercises/practice/proverb/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/pythagorean-triplet/libs/exercism/test b/exercises/practice/pythagorean-triplet/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/pythagorean-triplet/libs/exercism/test
+++ b/exercises/practice/pythagorean-triplet/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/raindrops/libs/exercism/test b/exercises/practice/raindrops/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/raindrops/libs/exercism/test
+++ b/exercises/practice/raindrops/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/resistor-color-duo/libs/exercism/test b/exercises/practice/resistor-color-duo/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/resistor-color-duo/libs/exercism/test
+++ b/exercises/practice/resistor-color-duo/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/resistor-color/libs/exercism/test b/exercises/practice/resistor-color/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/resistor-color/libs/exercism/test
+++ b/exercises/practice/resistor-color/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/reverse-string/libs/exercism/test b/exercises/practice/reverse-string/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/reverse-string/libs/exercism/test
+++ b/exercises/practice/reverse-string/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/rna-transcription/libs/exercism/test b/exercises/practice/rna-transcription/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/rna-transcription/libs/exercism/test
+++ b/exercises/practice/rna-transcription/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/roman-numerals/libs/exercism/test b/exercises/practice/roman-numerals/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/roman-numerals/libs/exercism/test
+++ b/exercises/practice/roman-numerals/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/rotational-cipher/libs/exercism/test b/exercises/practice/rotational-cipher/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/rotational-cipher/libs/exercism/test
+++ b/exercises/practice/rotational-cipher/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/run-length-encoding/libs/exercism/test b/exercises/practice/run-length-encoding/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/run-length-encoding/libs/exercism/test
+++ b/exercises/practice/run-length-encoding/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/scrabble-score/libs/exercism/test b/exercises/practice/scrabble-score/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/scrabble-score/libs/exercism/test
+++ b/exercises/practice/scrabble-score/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/secret-handshake/libs/exercism/test b/exercises/practice/secret-handshake/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/secret-handshake/libs/exercism/test
+++ b/exercises/practice/secret-handshake/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/series/libs/exercism/test b/exercises/practice/series/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/series/libs/exercism/test
+++ b/exercises/practice/series/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/sieve/libs/exercism/test b/exercises/practice/sieve/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/sieve/libs/exercism/test
+++ b/exercises/practice/sieve/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/space-age/libs/exercism/test b/exercises/practice/space-age/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/space-age/libs/exercism/test
+++ b/exercises/practice/space-age/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/spiral-matrix/libs/exercism/test b/exercises/practice/spiral-matrix/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/spiral-matrix/libs/exercism/test
+++ b/exercises/practice/spiral-matrix/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/square-root/libs/exercism/test b/exercises/practice/square-root/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/square-root/libs/exercism/test
+++ b/exercises/practice/square-root/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/strain/libs/exercism/test b/exercises/practice/strain/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/strain/libs/exercism/test
+++ b/exercises/practice/strain/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/sum-of-multiples/libs/exercism/test b/exercises/practice/sum-of-multiples/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/sum-of-multiples/libs/exercism/test
+++ b/exercises/practice/sum-of-multiples/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/triangle/libs/exercism/test b/exercises/practice/triangle/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/triangle/libs/exercism/test
+++ b/exercises/practice/triangle/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/trinary/libs/exercism/test b/exercises/practice/trinary/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/trinary/libs/exercism/test
+++ b/exercises/practice/trinary/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/two-fer/libs/exercism/test b/exercises/practice/two-fer/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/two-fer/libs/exercism/test
+++ b/exercises/practice/two-fer/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/word-count/libs/exercism/test b/exercises/practice/word-count/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/word-count/libs/exercism/test
+++ b/exercises/practice/word-count/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/exercises/practice/yacht/libs/exercism/test b/exercises/practice/yacht/libs/exercism/test
index 270681f..4997064 100644
--- a/exercises/practice/yacht/libs/exercism/test
+++ b/exercises/practice/yacht/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n -- 
diff --git a/libs/exercism/test b/libs/exercism/test
index 270681f..4997064 100644
--- a/libs/exercism/test
+++ b/libs/exercism/test
@@ -152,6 +152,14 @@ true var, run-test
    G:null? nip if test-passed else test-failed then 
 ;
 
+: not-null? \ s w --
+   run-test? !if drop test-skipped ;; then
+   w:exec
+   2 check-depth
+   null swap dup     \ so test-failed can show actual and expected
+   G:null? not nip if test-passed else test-failed then 
+;
+
 : SKIP-REST-OF-TESTS false run-test ! ;
 
 : tests \ n --