Go Testing
Quick Reference
| Pattern |
Use When |
t.Error |
Default — report failure, keep running |
t.Fatal |
Setup failed or continuing is meaningless |
cmp.Diff |
Comparing structs, slices, maps, protos |
| Table-driven |
Many cases share identical logic |
| Subtests |
Need filtering, parallel execution, or naming |
t.Helper() |
Any test helper function (call as first statement) |
t.Cleanup() |
Teardown in helpers instead of defer |
Useful Test Failures
Normative: Test failures must be diagnosable without reading the test
source.
Every failure message must include: function name, inputs, actual (got), and
expected (want). Use the format YourFunc(%v) = %v, want %v.
t.Errorf("Add(2, 3) = %d, want %d", got, 5)
t.Errorf("got %d, want %d", got, 5)
Always print got before want: got %v, want %v — never reversed.
No Assertion Libraries
Normative: Do not use assertion libraries. Use cmp.Diff for complex
comparisons.
if diff := cmp.Diff(want, got); diff != "" {
t.Errorf("GetPost() mismatch (-want +got):\n%s", diff)
}
For protocol buffers, add protocmp.Transform() as a cmp option. Always
include the direction key (-want +got) in diff messages. Avoid comparing
JSON/serialized output — compare semantically instead.
Read references/TEST-HELPERS.md when writing
custom comparison helpers or domain-specific test utilities.
t.Error vs t.Fatal
Normative: Use t.Error by default to report all failures in one run.
Use t.Fatal only when continuing is impossible.
Choose t.Fatal when:
- Setup fails (DB connection, file load)
- The next assertion depends on the previous one succeeding (e.g., decode after
encode)
Never call t.Fatal/t.FailNow from a goroutine other than the test
goroutine — use t.Error instead.
Read references/TEST-HELPERS.md when writing
helpers that need to choose between t.Error and t.Fatal, or for detailed
examples of both.
Table-Driven Tests
See assets/table-test-template.go when scaffolding a new table-driven test and need the canonical struct, loop, and subtest layout.
Advisory: Use table-driven tests when many cases share identical logic.
Use table tests when: all cases run the same code path with no conditional
setup, mocking, or assertions. A single shouldErr bool is acceptable.
Don't use table tests when: cases need complex setup, conditional mocking,
or multiple branches — write separate test functions instead.
Key rules:
- Use field names when cases span many lines or have same-type adjacent fields
- Include inputs in failure messages — never identify rows by index
Read references/TABLE-DRIVEN-TESTS.md
when writing table-driven tests, subtests, or parallel tests.
Validation: After generating or modifying tests, run go test -run TestXxx -v to verify the tests compile and pass. Fix any compilation errors before proceeding.
Test Helpers
Normative: Test helpers must call t.Helper() first and use t.Cleanup()
for teardown.
func setupTestDB(t *testing.T) *sql.DB {
t.Helper()
db, err := sql.Open("sqlite3", ":memory:")
if err != nil {
t.Fatalf("Could not open database: %v", err)
}
t.Cleanup(func() { db.Close() })
return db
}
Read references/TEST-HELPERS.md when writing
test helpers, cleanup functions, or custom comparison utilities.
Test Error Semantics
Advisory: Test error semantics, not error message strings.
if err.Error() != "invalid input" { ... }
if !errors.Is(err, ErrInvalidInput) { ... }
For simple presence checks when specific semantics don't matter:
if gotErr := err != nil; gotErr != tt.wantErr {
t.Errorf("f(%v) error = %v, want error presence = %t", tt.input, err, tt.wantErr)
}
Test Organization
Read references/TEST-ORGANIZATION.md when
working with test doubles, choosing test package placement, or scoping test
setup.
Read references/VALIDATION-APIS.md when
designing reusable test validation functions.
Integration Testing
Read references/INTEGRATION.md when writing
TestMain, acceptance tests, or tests that need real HTTP/RPC transports.
Available Scripts
scripts/gen-table-test.sh — Generates a table-driven test scaffold
bash scripts/gen-table-test.sh ParseConfig config > config/parse_config_test.go
bash scripts/gen-table-test.sh --parallel ParseConfig config
bash scripts/gen-table-test.sh --output config/parse_config_test.go ParseConfig config
Related Skills
- Error testing: See go-error-handling when testing error semantics with
errors.Is/errors.As or sentinel errors
- Interface mocking: See go-interfaces when creating test doubles by implementing interfaces at the consumer side
- Naming test functions: See go-naming when naming test functions, subtests, or test helper utilities
- Linter integration: See go-linting when running linters alongside tests in CI or pre-commit hooks
