package mocks import ( "errors" "testing" ) func TestWriter(t *testing.T) { t.Run("Write", func(t *testing.T) { expected := errors.New("mocked error") r := &Writer{ MockWrite: func(b []byte) (int, error) { return 0, expected }, } b := make([]byte, 128) count, err := r.Write(b) if !errors.Is(err, expected) { t.Fatal("unexpected error", err) } if count != 0 { t.Fatal("unexpected count", count) } }) }