| name | go/testing |
| description | Go testing patterns with stdlib testing package. Table-driven tests, subtests, test helpers, function-based mocks. Extends core/testing with Go-specific implementations.
|
Go Testing
Use stdlib testing package. No frameworks needed — testing + t.Run + t.Helper is sufficient.
Table-Driven Tests
Default pattern for testing multiple cases:
func TestParseAmount(t *testing.T) {
tests := []struct {
name string
input string
want int64
wantErr bool
}{
{name: "whole dollars", input: "42", want: 4200},
{name: "with cents", input: "42.50", want: 4250},
{name: "negative", input: "-10", wantErr: true},
{name: "empty string", input: "", wantErr: true},
}
for _, testCase := range tests {
t.Run(testCase.name, func(t *testing.T) {
got, err := ParseAmount(testCase.input)
if testCase.wantErr {
if err == nil { t.Fatal("expected error, got nil") }
return
}
if err != nil { t.Fatalf("unexpected error: %v", err) }
if got != testCase.want {
t.Errorf("ParseAmount(%q) = %d, want %d", testCase.input, got, testCase.want)
}
})
}
}
Guidelines: descriptive name first, got/want convention, t.Fatal for setup failures, t.Error for assertions.
Test Helpers
func assertNoError(t *testing.T, err error) {
t.Helper()
if err != nil { t.Fatalf("unexpected error: %v", err) }
}
func assertEqual[T comparable](t *testing.T, got, want T) {
t.Helper()
if got != want { t.Errorf("got %v, want %v", got, want) }
}
Setup and Teardown
func setupTestDB(t *testing.T) *sql.DB {
t.Helper()
db, err := sql.Open("postgres", testDSN)
if err != nil { t.Fatal(err) }
t.Cleanup(func() { db.Close() })
return db
}
Use testdata/ directories for test fixtures (Go ignores them during builds).
Function-Based Mocks
Recommended pattern — maximum flexibility per test:
type UserRepositoryFunc struct {
FindByIDFunc func(ctx context.Context, id string) (*User, error)
SaveFunc func(ctx context.Context, user *User) error
}
var _ UserRepository = (*UserRepositoryFunc)(nil)
func (m *UserRepositoryFunc) FindByID(ctx context.Context, id string) (*User, error) {
return m.FindByIDFunc(ctx, id)
}
func (m *UserRepositoryFunc) Save(ctx context.Context, user *User) error {
return m.SaveFunc(ctx, user)
}
Usage:
repo := &UserRepositoryFunc{
FindByIDFunc: func(_ context.Context, id string) (*User, error) {
if id == "user-1" { return &User{ID: "user-1"}, nil }
return nil, ErrNotFound
},
SaveFunc: func(_ context.Context, user *User) error {
savedUser = user
return nil
},
}
Test File Organization
package foo_test for black-box tests (preferred)package foo for white-box tests (when needed)- Unit tests co-located with code
- Integration tests in
test-integration/ directory
Anti-Patterns
- Testing private functions — test public API only
- Test frameworks when not established — stdlib covers 99% of needs
- Heavy mocking frameworks — use function-based mocks
time.Sleep() for sync — use channels or WaitGroups- Not using
t.Helper() — needed for accurate failure line numbers
- Assertions in loops without
t.Run — use subtests
Verification
