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| -rw-r--r-- | claude-rules/testing.md | 22 |
1 files changed, 15 insertions, 7 deletions
diff --git a/claude-rules/testing.md b/claude-rules/testing.md index a6bc1df..b2ff606 100644 --- a/claude-rules/testing.md +++ b/claude-rules/testing.md @@ -158,13 +158,21 @@ the specific case choice. - Never hardcode dates or times — generate them relative to `now()` - No reliance on test execution order - No flaky network calls in unit tests -- Time/clock-mocking helpers must not call the primitives they're - mocking (infinite recursion), and must not `let`-bind over a - `defvar` or other globally-defined symbol (the binding shadows the - global only inside the test scope, so production code that reads the - symbol gets the original value, not the mock — silent test miss). - Mock by redefining at the symbol's definition site or via the - language's first-class mocking primitive. +- Time/clock-mocking helpers must avoid two recurring failure modes: + - *Infinite recursion.* The helper must not call the primitive it's + replacing. If the mock for `now()` calls `now()`, the test stack + overflows. Compute the mock value from a fixed source (a captured + instant, an injected fake clock). + - *Scope-shadowing without reach.* A mock that only exists inside + the test function won't affect production code that reads the + symbol through its canonical path. Replace the symbol at its + definition site (monkey-patch the module attribute in Python, + redefine the global in Lisp, swap the package-level binding in + Go, replace the named export in JavaScript) — or inject a fake + via dependency-inversion. Don't lean on scope-shadowing + primitives (Lisp `let`, Python local rebind, JS shadowed `let`) + that fence the mock to the test's lexical scope; production code + won't see them and the test passes against the real clock. ### Performance - Unit tests: <100ms each |