feat(throw):#3 added ApplicationError

README.md

@@ -105,5 +105,32 @@ fmt.Println(cause) => password mismatch
 
 ```
 
+## Working with [Errors](https://blog.golang.org/go1.13-errors) package
+
+How to raise an `ApplicationError` with predefined error variables?
+
+```
+var ErrInvalidFormat = errors.New("[conf]invalid format")
+
+func ReadConfig()  (*Config,error) {
+   //...
+   return nil, Throw(ErrInvalidFormat, cfgFile)
+
+}
+
+func main() {
+
+cfg, err := ReadConfig() 
+
+if errors.Is(err, ErrInvalidFormat) {
+    panic(err)
+}
+
+}
+
+```
+
+See [Unit Tests](throw_test.go) for more examples.
+
 
 

throw.go

@@ -0,0 +1,50 @@
+package errors
+
+import "strings"
+
+// ApplicationError an appliction error with predifined error variable and detail message
+type ApplicationError struct {
+	// Inner inner error
+	Inner error
+	// MsgList detail message
+	MsgList []string
+}
+
+// Error implement error.Error
+func (e *ApplicationError) Error() string {
+	if e == nil {
+		return ""
+	}
+
+	if e.Inner != nil && e.MsgList != nil {
+		return e.Inner.Error() + ": " + strings.Join(e.MsgList, " ")
+	} else if e.Inner != nil {
+		return e.Inner.Error()
+	} else {
+		return strings.Join(e.MsgList, " ")
+	}
+
+}
+
+// Unwrap implement error.Unwrap
+func (e *ApplicationError) Unwrap() error {
+	if e == nil {
+		return nil
+	}
+
+	if e.Inner != nil {
+		return e.Inner
+	}
+
+	return e
+}
+
+// Throw create an application error with prefinded error variable and message
+// example
+//    errors.Throw(ErrInvalidParameter, "bloober_id is missing")
+func Throw(inner error, msgList ...string) error {
+	return &ApplicationError{
+		Inner:   inner,
+		MsgList: msgList,
+	}
+}

throw_test.go

@@ -0,0 +1,40 @@
+package errors
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestThrowIs(t *testing.T) {
+
+	errIs := errors.New("Is")
+
+	errIsNot := errors.New("Is not")
+
+	err := Throw(errIs, "", "errors.Is works")
+
+	require.ErrorIs(t, err, errIs)
+	require.Equal(t, false, errors.Is(err, errIsNot))
+}
+
+func TestThrowUnwrap(t *testing.T) {
+
+	inner := errors.New("Inner")
+
+	err := Throw(inner, "errors.Unwrap works")
+
+	require.Equal(t, inner, errors.Unwrap(err))
+}
+
+func TestThrowAs(t *testing.T) {
+
+	inner := errors.New("Inner")
+
+	err := Throw(inner, "errors.As works")
+
+	var appErr *ApplicationError
+
+	require.Equal(t, true, errors.As(err, &appErr))
+}