golang-testing-patterns

name	golang-testing-patterns
description	Modern Go testing patterns including table-driven tests, subtests, test organization, and best practices. Use when writing or refactoring tests, implementing test coverage, or when the user asks about Go testing approaches.

Go Testing Patterns

Modern testing patterns for Go following 2025-2026 best practices.

Table-Driven Tests

The idiomatic Go approach for comprehensive testing.

Basic structure:

func TestFeature(t *testing.T) {
	tests := []struct {
		name     string
		input    string
		expected int
		wantErr  bool
	}{
		{
			name:     "valid input",
			input:    "hello",
			expected: 5,
			wantErr:  false,
		},
		{
			name:     "empty input",
			input:    "",
			expected: 0,
			wantErr:  true,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			got, err := ProcessString(tt.input)
			
			if tt.wantErr {
				if err == nil {
					t.Errorf("expected error, got nil")
				}
				return
			}
			
			if err != nil {
				t.Fatalf("unexpected error: %v", err)
			}
			
			if got != tt.expected {
				t.Errorf("got %d, want %d", got, tt.expected)
			}
		})
	}
}

Using Subtests with t.Run()

Benefits:

• Clear failure messages showing which case failed
• Can run specific tests: go test -run TestFeature/valid_input
• Parallel execution support

Pattern:

for _, tt := range tests {
	t.Run(tt.name, func(t *testing.T) {
		t.Parallel() // Run subtests in parallel
		// ... test logic
	})
}

Test Organization

File structure:

• Tests live alongside code: service.go → service_test.go
• Integration tests in separate package: service_integration_test.go
• Shared test utilities: test/util/ or testutil/

Test function naming:

// Unit tests
func TestSessionService_CreateSession(t *testing.T) {}
func TestSessionService_CreateSession_ValidationError(t *testing.T) {}

// Integration tests
func TestSessionService_Integration(t *testing.T) {}

Setup and Teardown

Using t.Cleanup():

func TestWithCleanup(t *testing.T) {
	// Setup
	db := setupTestDB(t)
	t.Cleanup(func() {
		db.Close() // Always runs, even if test fails
	})
	
	// Test logic
	// ...
}

Setup once for all subtests:

func TestSuite(t *testing.T) {
	// Shared setup
	db := setupTestDB(t)
	t.Cleanup(func() { db.Close() })
	
	t.Run("test1", func(t *testing.T) {
		// Uses shared db
	})
	
	t.Run("test2", func(t *testing.T) {
		// Uses shared db
	})
}

Testing Database Operations

Transaction-based isolation:

func TestDatabaseOperation(t *testing.T) {
	db := setupTestDB(t)
	
	tests := []struct {
		name string
		// ... test fields
	}{
		// ... test cases
	}
	
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// Each subtest gets fresh data
			tx, _ := db.Begin()
			t.Cleanup(func() { tx.Rollback() })
			
			// Use tx for test operations
			// ...
		})
	}
}

Error Testing Patterns

Check error occurrence:

if tt.wantErr {
	if err == nil {
		t.Errorf("expected error, got nil")
	}
	return
}

if err != nil {
	t.Fatalf("unexpected error: %v", err)
}

Check specific error:

if !errors.Is(err, ErrNotFound) {
	t.Errorf("expected ErrNotFound, got %v", err)
}

Check error message — prefer exact match:

Use Equal / direct comparison for error messages you control. Only fall back to Contains when the message includes third-party or runtime text you don't own.

// GOOD — exact match on our own error message
assert.Equal(t, "missing required field 'name'", err.Error())

// GOOD — unwrap first when error is wrapped (e.g. LoadError)
var loadErr *LoadError
require.ErrorAs(t, err, &loadErr)
assert.Equal(t, "missing required field 'name'", loadErr.Err.Error())

// OK — Contains is justified when part of the message comes from a third-party
// library (e.g. yaml.Unmarshal, sql driver) whose text we don't control.
assert.Contains(t, err.Error(), "invalid YAML")

Test Helpers

Creating test data:

func newTestSession(t *testing.T, overrides ...func(*ent.AlertSession)) *ent.AlertSession {
	t.Helper() // Ensures stack traces point to the caller
	
	session := &ent.AlertSession{
		ID:        "test-123",
		Status:    "pending",
		StartedAt: time.Now(),
	}
	
	for _, override := range overrides {
		override(session)
	}
	
	return session
}

// Usage
session := newTestSession(t, func(s *ent.AlertSession) {
	s.Status = "completed"
})

Mocking and Interfaces

Interface-based testing:

type SessionRepository interface {
	GetByID(ctx context.Context, id string) (*Session, error)
}

// In test
type mockSessionRepo struct {
	sessions map[string]*Session
}

func (m *mockSessionRepo) GetByID(ctx context.Context, id string) (*Session, error) {
	s, ok := m.sessions[id]
	if !ok {
		return nil, ErrNotFound
	}
	return s, nil
}

Testing Patterns for TARSy

Service layer tests:

func TestSessionService_CreateSession(t *testing.T) {
	// Setup test database with cleanup
	client, _ := test.SetupTestDatabase(t)
	service := services.NewSessionService(client)
	
	tests := []struct {
		name       string
		req        models.CreateSessionRequest
		wantErr    bool
		wantErrMsg string
	}{
		{
			name: "valid session",
			req: models.CreateSessionRequest{
				SessionID: "sess-123",
				// ... other fields
			},
			wantErr: false,
		},
		{
			name: "missing session ID",
			req: models.CreateSessionRequest{
				SessionID: "",
			},
			wantErr:    true,
			wantErrMsg: "session_id is required",
		},
	}
	
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			ctx := t.Context()
			session, err := service.CreateSession(ctx, tt.req)
			
			if tt.wantErr {
				if err == nil {
					t.Fatal("expected error, got nil")
				}
				if tt.wantErrMsg != "" {
					// Exact match — we own this error message
					if err.Error() != tt.wantErrMsg {
						t.Errorf("error = %q, want %q", err.Error(), tt.wantErrMsg)
					}
				}
				return
			}
			
			if err != nil {
				t.Fatalf("unexpected error: %v", err)
			}
			
			if session.ID != tt.req.SessionID {
				t.Errorf("session ID = %q, want %q", session.ID, tt.req.SessionID)
			}
		})
	}
}

Quick Reference

When to use table-driven tests:

• Multiple similar test cases with different inputs/outputs
• Testing edge cases and validation
• Any test with more than 2-3 cases

When to skip table-driven tests:

• Single, unique test case
• Complex setup that varies significantly between cases
• Integration tests with sequential dependencies

Parallel testing:

t.Parallel() // Use for fast, independent tests
// Don't use for: database tests, shared state, rate-limited APIs

Assertions:

• Use t.Errorf() for non-fatal assertions
• Use t.Fatalf() when continuing would panic or is meaningless
• Always include both got and want in error messages
• Prefer Equal over Contains for values you control (catches regressions, documents the exact contract)
• Reserve Contains for third-party/runtime strings you don't own