[Errors] Add WithError() to Error interface in order to wrap source e…

…rror.

errors/error.go

@@ -23,6 +23,7 @@ type Error interface {
 	WithMessage(format string, args ...interface{}) Error
 	WithKind(string) Error
 	WithStatus(int) Error
+	WithError(error) Error
 }
 
 // FullError is a concrete error that implements the Error interface
@@ -126,6 +127,14 @@ func (e *FullError) WithKind(kind string) Error {
 	return e
 }
 
+// WithError wrap source error.
+func (e *FullError) WithError(err error) Error {
+	e.sourceErr = err
+	e.errorMessage = err.Error()
+
+	return e
+}
+
 // HttpError is used to json.Marshal or xml.Marshal FullError.
 // You can use it to decode an incoming error.
 type HttpError struct {

errors/error_test.go

@@ -38,4 +38,10 @@ func TestErr(t *testing.T) {
 	assert.Equal(t, expectedKind, err.Kind())
 	assert.Equal(t, expectedMessage, err.Message())
 	assert.Equal(t, expectedStatusCode, err.StatusCode())
+
+	otherError := errors.New("this is an another error")
+
+	err = err.WithError(otherError)
+
+	assert.Equal(t, otherError.Error(), err.Error())
 }