Ahnii,

Ever struggled with testing your Cobra CLI applications? I recently refactored one of my projects to use dependency injection, and it made testing so much easier. Let me show you how!

Why Dependency Injection? (2 minutes)

Key benefits for CLI apps:

  • Easier to mock dependencies
  • More testable code
  • Cleaner separation of concerns
  • Flexible configuration

Basic Setup (5 minutes)

Here’s our basic CLI structure with DI:

type AppDependencies struct {
    Logger  Logger
    Config  Config
    Client  HTTPClient
}

func NewRootCmd(deps *AppDependencies) *cobra.Command {
    cmd := &cobra.Command{
        Use:   "mycli",
        Short: "My CLI application",
        RunE: func(cmd *cobra.Command, args []string) error {
            return runRoot(deps, args)
        },
    }
    return cmd
}

Testing Strategy (10 minutes)

  1. Mock Dependencies
type MockLogger struct {
    mock.Mock
}

func TestRootCommand(t *testing.T) {
    mockLogger := &MockLogger{}
    deps := &AppDependencies{
        Logger: mockLogger,
    }
    
    cmd := NewRootCmd(deps)
    assert.NotNil(t, cmd)
}
  1. Test Command Execution
func TestCommandExecution(t *testing.T) {
    deps := setupTestDependencies()
    cmd := NewRootCmd(deps)
    
    output, err := executeCommand(cmd, "arg1", "--flag=value")
    assert.NoError(t, err)
    assert.Contains(t, output, "expected output")
}

Best Practices

  • Keep dependencies minimal and focused
  • Use interfaces for flexibility
  • Test edge cases thoroughly
  • Mock external services

Common Patterns

  1. Configuration Injection
func NewConfig() *Config {
    return &Config{
        // Default values
    }
}
  1. Logger Injection
type Logger interface {
    Info(msg string, args ...interface{})
    Error(msg string, args ...interface{})
}

Wrapping Up

Dependency injection might seem like overhead at first, but it pays off in testability and maintainability. Start small and refactor as needed.

How do you handle testing in your CLI applications? Have you tried dependency injection? Share your experiences below!

Baamaapii 👋