package parser import ( "errors" "testing" "github.com/stretchr/testify/require" ) type customErr struct { err string } func (e customErr) Error() string { return e.err } func TestCombineErrors(t *testing.T) { err := combineErrors(nil, errors.New("first"), nil, customErr{"second"}) require.EqualError(t, err, "first\nsecond") err = customErr{"custom error"} require.Equal(t, err, combineErrors(nil, err, nil)) require.Nil(t, combineErrors(nil, nil, nil)) }