Update some uses of errors.Cause() to errors.Is()

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit bb7ef2cb3a)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli-plugins/manager/error.go

@@ -25,6 +25,11 @@ func (e *pluginError) Cause() error {
 	return e.cause
 }
 
+// Unwrap provides compatibility for Go 1.13 error chains.
+func (e *pluginError) Unwrap() error {
+	return e.cause
+}
+
 // MarshalText marshalls the pluginError into a textual form.
 func (e *pluginError) MarshalText() (text []byte, err error) {
 	return []byte(e.cause.Error()), nil

cli-plugins/manager/error_test.go

@@ -16,7 +16,7 @@ func TestPluginError(t *testing.T) {
 	inner := fmt.Errorf("testing")
 	err = wrapAsPluginError(inner, "wrapping")
 	assert.Error(t, err, "wrapping: testing")
-	assert.Equal(t, inner, errors.Cause(err))
+	assert.Assert(t, errors.Is(err, inner))
 
 	actual, err := yaml.Marshal(err)
 	assert.NilError(t, err)

cli/config/config_test.go

@@ -80,7 +80,7 @@ func TestEmptyFile(t *testing.T) {
 	assert.NilError(t, err)
 
 	_, err = Load(tmpHome)
-	assert.Equal(t, errors.Cause(err), io.EOF)
+	assert.Assert(t, errors.Is(err, io.EOF))
 	assert.ErrorContains(t, err, ConfigFileName)
 }