Fix #90

checks/generators/generators1.py

@@ -1,4 +1,4 @@
-assert list(count_up_to(4)) == [1, 2, 3, 4]
-assert list(count_up_to(1)) == [1]
-assert list(count_up_to(0)) == []
+assert list(count_up_to(4)) == [1, 2, 3, 4], f"expected [1, 2, 3, 4], got {list(count_up_to(4))}"
+assert list(count_up_to(1)) == [1], f"expected [1], got {list(count_up_to(1))}"
+assert list(count_up_to(0)) == [], f"expected [], got {list(count_up_to(0))}"
 print("generators1 ✓")

checks/generators/generators3.py

@@ -1,4 +1,4 @@
 assert collected == [2, 4, 6, 8], f"expected [2, 4, 6, 8], got {collected}"
-assert list(evens_up_to(5)) == [2, 4]
-assert list(evens_up_to(1)) == []
+assert list(evens_up_to(5)) == [2, 4], f"expected [2, 4], got {list(evens_up_to(5))}"
+assert list(evens_up_to(1)) == [], f"expected [], got {list(evens_up_to(1))}"
 print("generators3 ✓")

checks/generators/generators6.py

@@ -3,6 +3,6 @@
 )
 # Confirm the generator really is infinite: pull 1000 values.
 big = list(itertools.islice(natural_numbers(), 1000))
-assert len(big) == 1000
-assert big[-1] == 1000
+assert len(big) == 1000, f"expected 1000 values, got {len(big)}"
+assert big[-1] == 1000, f"expected last value 1000, got {big[-1]}"
 print("generators6 ✓")

checks/generators/generators7.py

@@ -6,6 +6,6 @@
 )
 # Confirm more terms keep coming.
 first15 = list(itertools.islice(fibonacci(), 15))
-assert len(first15) == 15
-assert first15[-1] == 377
-print("generators7 ✓")
+assert len(first15) == 15, f"expected 15 terms in the sequence, got {len(first15)}"
+assert first15[-1] == 377, f"expected the 15th term to be 377, got {first15[-1]}"
+print("generators7 \u2713")

checks/generators/generators8.py

@@ -1,8 +1,8 @@
-assert list(Countdown(3)) == [3, 2, 1]
-assert list(Countdown(1)) == [1]
-assert list(Countdown(5)) == [5, 4, 3, 2, 1]
+assert list(Countdown(3)) == [3, 2, 1], f"expected [3, 2, 1], got {list(Countdown(3))}"
+assert list(Countdown(1)) == [1], f"expected [1], got {list(Countdown(1))}"
+assert list(Countdown(5)) == [5, 4, 3, 2, 1], f"expected [5, 4, 3, 2, 1], got {list(Countdown(5))}"
 # Should be re-iterable: a fresh iteration each time.
 cd = Countdown(3)
-assert list(cd) == [3, 2, 1]
-assert list(cd) == [3, 2, 1]
-print("generators8 ✓")
+assert list(cd) == [3, 2, 1], f"expected a fresh iteration [3, 2, 1], got {list(cd)}"
+assert list(cd) == [3, 2, 1], f"expected the second iteration to replay [3, 2, 1], got {list(cd)}"
+print("generators8 \u2713")

tests/test_generators_assertion_messages.py

@@ -0,0 +1,26 @@
+import ast
+import pathlib
+
+
+CHECKS = [
+    "checks/generators/generators1.py",
+    "checks/generators/generators3.py",
+    "checks/generators/generators6.py",
+    "checks/generators/generators7.py",
+    "checks/generators/generators8.py",
+]
+
+
+def _asserts_without_message(path):
+    tree = ast.parse(pathlib.Path(path).read_text())
+    missing = []
+    for node in ast.walk(tree):
+        if isinstance(node, ast.Assert) and node.msg is None:
+            missing.append(node.lineno)
+    return missing
+
+
+def test_generators_checks_have_actionable_assertion_messages():
+    for path in CHECKS:
+        missing = _asserts_without_message(path)
+        assert missing == [], f"{path} has asserts without messages at lines {missing}"