Added tests for isAppEngineRetryableError (#4470) (#8409)

Signed-off-by: Modular Magician <[email protected]>

.changelog/4470.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+appengine: added retry for P4SA propagation delay
+```

google/error_retry_predicates.go

@@ -246,7 +246,7 @@ func isAppEngineRetryableError(err error) (bool, string) {
 		if gerr.Code == 409 && strings.Contains(strings.ToLower(gerr.Body), "operation is already in progress") {
 			return true, "Waiting for other concurrent App Engine changes to finish"
 		}
-		if gerr.Code == 404 && strings.Contains(strings.ToLower(gerr.Body), "unable to retrieve P4SA") {
+		if gerr.Code == 404 && strings.Contains(strings.ToLower(gerr.Body), "unable to retrieve p4sa") {
 			return true, "Waiting for P4SA propagation to GAIA"
 		}
 	}

google/error_retry_predicates_test.go

@@ -0,0 +1,51 @@
+package google
+
+import (
+	"testing"
+
+	"google.golang.org/api/googleapi"
+)
+
+func TestIsAppEngineRetryableError_operationInProgress(t *testing.T) {
+	err := googleapi.Error{
+		Code: 409,
+		Body: "Operation is already in progress",
+	}
+	isRetryable, _ := isAppEngineRetryableError(&err)
+	if !isRetryable {
+		t.Errorf("Error not detected as retryable")
+	}
+}
+
+func TestIsAppEngineRetryableError_p4saPropagation(t *testing.T) {
+	err := googleapi.Error{
+		Code: 404,
+		Body: "Unable to retrieve P4SA: [[email protected]] from GAIA. Could be GAIA propagation delay or request from deleted apps.",
+	}
+	isRetryable, _ := isAppEngineRetryableError(&err)
+	if !isRetryable {
+		t.Errorf("Error not detected as retryable")
+	}
+}
+
+func TestIsAppEngineRetryableError_missingPage(t *testing.T) {
+	err := googleapi.Error{
+		Code: 404,
+		Body: "Missing page",
+	}
+	isRetryable, _ := isAppEngineRetryableError(&err)
+	if isRetryable {
+		t.Errorf("Error incorrectly detected as retryable")
+	}
+}
+
+func TestIsAppEngineRetryableError_serverError(t *testing.T) {
+	err := googleapi.Error{
+		Code: 500,
+		Body: "Unable to retrieve P4SA because of a bad thing happening",
+	}
+	isRetryable, _ := isAppEngineRetryableError(&err)
+	if isRetryable {
+		t.Errorf("Error incorrectly detected as retryable")
+	}
+}