Fix #5. Supports methods Cause and Unwrap

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Valkyrie - Changelog
 
+## v0.1.0 (2020-MAY-27)
+- supports method Cause
+- supports method Unwrap for Go 1.13 error chains
+
 ## v0.0.1 (2018-JAN-19)
 
 - initial fork commit

multierror.go

@@ -43,3 +43,20 @@ func (m *MultiError) Error() string {
 
 	return strings.Join(formattedError, ", ")
 }
+
+// Cause returns the first original error.
+func (m *MultiError) Cause() error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	if len(m.errs) == 0 {
+		return nil
+	}
+
+	return m.errs[0]
+}
+
+// Unwrap provides compatibility for go 1.13 error chains.
+func (m *MultiError) Unwrap() error {
+	return m.Cause()
+}

multierror_test.go

@@ -56,3 +56,29 @@ func TestMultiErrorWhileConcurrentPushShouldNotPanic(t *testing.T) {
 	}
 	assert.NotPanics(t, concurrentPushAndErrors)
 }
+
+func TestMultiError_Cause(t *testing.T) {
+	me := &MultiError{}
+	assert.NoError(t, me.Cause())
+
+	me.Push("one")
+	me.Push("two")
+	me.Push("three")
+
+	err := me.Cause()
+	assert.Error(t, err)
+	assert.Equal(t, "one", err.Error())
+}
+
+func TestMultiError_Unwrap(t *testing.T) {
+	me := &MultiError{}
+	assert.NoError(t, me.Unwrap())
+
+	me.Push("one")
+	me.Push("two")
+	me.Push("three")
+
+	err := me.Unwrap()
+	assert.Error(t, err)
+	assert.Equal(t, "one", err.Error())
+}