errors: fix package example

The example in example_test.go requires that the whole file be
displayed; the addition of ExampleAs meant that only the body of the
package example function was shown, rather than the surrounding context.

This change moves ExampleAs to the file wrap_test.go file, restoring the
package example to its former glory.

Update #31716

Change-Id: Id0ea77bc06023b239a63c1d6a7c8b3c1dae91ce9
Reviewed-on: https://go-review.googlesource.com/c/go/+/179737
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
Reviewed-by: Jean de Klerk <deklerk@google.com>
Run-TryBot: Benny Siegert <bsiegert@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/errors/wrap_test.go b/src/errors/wrap_test.go
index 2055316756..d349414527 100644
--- a/src/errors/wrap_test.go
+++ b/src/errors/wrap_test.go
@@ -218,3 +218,17 @@ func (errorUncomparable) Is(target error) bool {
 	_, ok := target.(errorUncomparable)
 	return ok
 }
+
+func ExampleAs() {
+	if _, err := os.Open("non-existing"); err != nil {
+		var pathError *os.PathError
+		if errors.As(err, &pathError) {
+			fmt.Println("Failed at path:", pathError.Path)
+		} else {
+			fmt.Println(err)
+		}
+	}
+
+	// Output:
+	// Failed at path: non-existing
+}