gofasta g mock

Walks the project’s interface declarations and emits a testify/mock implementation under testutil/mocks/<snake>_mock.go. The generated mock:

• Embeds testify/mock.Mock so every method gets On(...).Return(...) ergonomics.
• Includes a compile-time assertion (var _ iface.OrderService = (*OrderServiceMock)(nil)) so a future interface change breaks the build rather than silently producing a non-conforming mock.
• Picks the right testify accessor per return type (Error, String, Int, Bool, or a nil-safe typed Get assertion for pointer / slice / map / qualified-type returns).
• Is gofmt-clean out of the box.

Two operating modes: generate one mock for a named interface, or --all to refresh every mock under the standard interface dirs.

Usage

gofasta g mock [InterfaceName] [flags]

The positional arg is the exact interface name (e.g. OrderService, UserRepositoryInterface). Omit it with --all to refresh every mock.

Flags

Examples

Generate one mock:

gofasta g mock OrderService
# → testutil/mocks/order_service_mock.go

Refresh every mock after changing several interfaces at once:

gofasta g mock --all

CI: detect mocks that haven’t been regenerated after an interface change:

gofasta g mock --all --check
# exit 0 → all mocks in sync
# exit !0 → MOCK_DRIFT — re-run without --check to update

CI: check one mock specifically:

gofasta g mock OrderService --check

Output shape

Given:

// app/services/interfaces/order_service.go
package interfaces
 
import "context"
 
type OrderService interface {
    Get(ctx context.Context, id string) (*Order, error)
    List(ctx context.Context) ([]*Order, error)
    Archive(ctx context.Context, id string) error
}

gofasta g mock OrderService writes:

// testutil/mocks/order_service_mock.go
// Code generated by `gofasta g mock`. DO NOT EDIT.
// Regenerate by running `gofasta g mock OrderService` (or `--all`).
 
package mocks
 
import (
    "context"
    "myapp/app/services/interfaces"
    "myapp/app/models"
    "github.com/stretchr/testify/mock"
)
 
// OrderServiceMock is a testify/mock implementation of interfaces.OrderService.
type OrderServiceMock struct {
    mock.Mock
}
 
var _ interfaces.OrderService = (*OrderServiceMock)(nil)
 
func (m *OrderServiceMock) Get(ctx context.Context, id string) (*models.Order, error) {
    args := m.Called(ctx, id)
    return func() *models.Order {
        if v := args.Get(0); v != nil {
            return v.(*models.Order)
        }
        return nil
    }(), args.Error(1)
}
 
func (m *OrderServiceMock) List(ctx context.Context) ([]*models.Order, error) {
    args := m.Called(ctx)
    return func() []*models.Order {
        if v := args.Get(0); v != nil {
            return v.([]*models.Order)
        }
        return nil
    }(), args.Error(1)
}
 
func (m *OrderServiceMock) Archive(ctx context.Context, id string) error {
    args := m.Called(ctx, id)
    return args.Error(0)
}

The pointer / slice / map / qualified-type returns are guarded with the if v := args.Get(...); v != nil { ... } shim so a nil return value doesn’t panic at runtime.

Where it looks

--all walks two directories:

• app/services/interfaces/
• app/repositories/interfaces/

Every interface declared in any *.go (not _test.go) file there is regenerated. Other directories aren’t scanned — interfaces defined elsewhere need the explicit form (gofasta g mock <Name>).

For the single-interface form, the same two directories are searched. An interface declared in both (rare) returns AMBIGUOUS_SYMBOL with the list of files.

Embedded interfaces

The initial release supports flat interfaces only. An interface that embeds another:

type AdminService interface {
    UserService                          // embedded — skipped
    PromoteToAdmin(ctx context.Context, userID string) error
}

Will generate a mock with PromoteToAdmin only; the embedded UserService methods are silently dropped. If you need to mock an embedded interface, define the flat version directly or compose mocks at the test site.

Drift detection (--check)

--check compares the generated bytes to the on-disk file. Differences (whitespace-normalized) trigger MOCK_DRIFT. Use this in CI to enforce that interface changes are accompanied by a mock regeneration:

# .github/workflows/ci.yml
- run: gofasta g mock --all --check

If it fails, the developer’s fix is gofasta g mock --all locally + commit the updated mock.

Error codes