Golang Testing

Priority: P0 (CRITICAL)

Core Rule Anchors

• [BE-TEST-01] Table-Driven Subtests for Equivalent Cases: Prefer table-driven tests ([]struct{ name, input, expected, expectErr } with t.Run) when functions have multiple equivalent inputs, boundary permutations, or repetitive setup. Distinct scenarios or diverging setup may remain separate test functions; 2-3 distinct cases are fine. Reviewers must not raise stylistic table-driven findings without a behavioral gap.
• [BE-TEST-02] Ban on Brittle SQLMock String Matching: Do not use sqlmock.ExpectQuery to regex-match raw SQL strings. Test pure domain business calculations directly, or use testcontainers-go for PostgreSQL repository verification.
• [BE-TEST-03] Ban on Shallow Assertions: Never assert only assert.NoError(t, err) or assert.NotNil(t, result) without inspecting returned domain struct fields, status codes, and invariants.
• [BE-TEST-04] Ban on Pass-Through Interface Mocks: Repositories and service handlers must test contract compliance and error mapping. Ban 1:1 pass-through mock echoing without contract assertions.
• [BE-TEST-05] Bug-First Regression Lock: Every PR fixing a bug ticket or with title fix(...) must introduce a test reproducing the defect prior to the fix.

Implementation Workflow

1. Write failing test first — Follow Red-Green-Refactor TDD workflow ([BE-TEST-05]).
2. Table-driven tests for equivalent inputs — For parameterized cases sharing setup, define test cases as a slice of structs with t.Run ([BE-TEST-01]).
3. Zero Volatile Fields for Struct Comparison — When asserting struct equality, zero out timestamps, dynamic IDs, or generated tokens before assert.Equal to prevent flaky assertions.
4. Mock via interfaces — Use DI and small, consumer-centric interfaces (1-3 methods) ([BE-TEST-04]). Prefer mockery for auto-generated mocks or manual mocks for simple cases.
5. Run parallel — Use t.Parallel() for non-sequential tests to speed up CI.
6. Clean up resources — Use t.Cleanup() to restore state or release DB/file resources.
7. Check coverage — Coverage is diagnostic and project-configured; verify risk-weighted critical paths rather than padding code for an arbitrary percentage.

See table-driven test examples

Tools & Naming

• Stdlib: testing package (TestXxx(t *testing.T), ExampleXxx()).
• Testify: Assertions (assert, require) and mocks.
• Mockery / GoMock: Auto-generate mocks for interfaces.
• Integration: Prefer testcontainers-go over raw SQL mock strings ([BE-TEST-02]).

Anti-Patterns

• [BE-TEST-01] No stylistic rewrites: Do not demand table-driven rewrites of passing tests unless 5+ repetitive blocks or a coverage gap exists.
• [BE-TEST-02] No raw SQL regex matching: Do not match SQL strings in mocks.
• [BE-TEST-03] No shallow assertions: Never assert only assert.NoError/NotNil without payload inspection.
• [BE-TEST-04] No pass-through mock echoing: Ban 1:1 mock echoing without contract assertions.
• [BE-TEST-05] No bug fix without reproduction test.
• No assert in loops: use t.Run subtests to isolate failures.
• No brittle assertions on volatile fields: normalize timestamps/dynamic IDs.
• No global mock state: define mocks locally within test scope.
• No skipping race detection: always run go test -race in CI.

References

• Table-Driven Tests
• Mocking Strategies