feat(errors): Added Group Errors (#106)

Signed-off-by: Flc゛ <four_leaf_clover@foxmail.com>

errors/group.go

@@ -0,0 +1,57 @@
+package errors
+
+import "errors"
+
+var multipleErrors = "multiple errors"
+
+type Group struct {
+	errors []error
+}
+
+func NewGroup() *Group {
+	return &Group{
+		errors: make([]error, 0),
+	}
+}
+
+func (g *Group) Add(errs ...error) *Group {
+	for _, err := range errs {
+		if err == nil {
+			continue
+		}
+
+		g.errors = append(g.errors, err)
+	}
+
+	return g
+}
+
+func (g *Group) Error() string {
+	return multipleErrors
+}
+
+func (g *Group) Errors() []error {
+	return g.errors
+}
+
+func (g *Group) Len() int {
+	return len(g.errors)
+}
+
+func (g *Group) Has(err error) bool {
+	for _, e := range g.errors {
+		if errors.Is(e, err) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (g *Group) First() error {
+	if len(g.errors) == 0 {
+		return nil
+	}
+
+	return g.errors[0]
+}

errors/group_test.go

@@ -0,0 +1,29 @@
+package errors
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	err1 = errors.New("err1")
+	err2 = errors.New("err2")
+	err3 = errors.New("err3")
+)
+
+func TestGroup(t *testing.T) {
+	g := NewGroup()
+
+	assert.Equal(t, 0, g.Len())
+	assert.Equal(t, g, g.Add(nil, err1, err2))
+
+	assert.Equal(t, 2, g.Len())
+	assert.Equal(t, multipleErrors, g.Error())
+	assert.Equal(t, []error{err1, err2}, g.Errors())
+	assert.True(t, g.Has(err1))
+	assert.True(t, g.Has(err2))
+	assert.False(t, g.Has(err3))
+	assert.Equal(t, err1, g.First())
+}