Unwrap pr suggestion

.travis.yml

@@ -2,5 +2,6 @@ language: go
 
 go:
  - "1.8.x"
- - "1.14.x"
- - tip
+ - "1.12.x"
+ - "1.13.x"
+ - "1.15.x"

error_is.go

@@ -0,0 +1,29 @@
+// +build go1.13
+
+package errorx
+
+import "errors"
+
+// Is implements the helper interface for errors.Is
+// It first checks if target is an *Error and uses IsOfType to check if e Is target.
+// If target is not an *Error, it instead iterates through the error chain until it reaches a non-*Error error (or nil)
+// and calls errors.Is on that error and target.
+func (e *Error) Is(target error) bool {
+// Check if target is an *Error, if so we can use IsOfType.
+t := Cast(target)
+if t != nil {
+return e.IsOfType(t.Type())
+}
+
+// target is not an *Error, so iterate through the error chain until nil or a non-*Error error is reached and use
+// errors.Is to check against that.
+cause := e
+for cause != nil {
+next := Cast(cause.Cause())
+if next == nil && cause.Cause() != nil {
+return errors.Is(cause.Cause(), target)
+}
+cause = next
+}
+return false
+}