Test that error rewriting works as intended

This commit adds a handful of tests to make sure errors in the
problematic formats are rewritten, and other errors are left alone.

I'm reluctant to test against the actual git providers, since that
would introduce a dependency on them. Thus, these tests won't guard
against the providers changing their messages.

Signed-off-by: Michael Bridgen <michael@weave.works>

controllers/git_error_test.go

@@ -0,0 +1,102 @@
+/*
+Copyright 2020, 2021 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package controllers
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestLibgit2ErrorTidy(t *testing.T) {
+	// this is what GitLab sends if the deploy key doesn't have write access
+	gitlabMessage := `remote: 
+remote: ========================================================================
+remote: 
+remote: This deploy key does not have write access to this project.
+remote: 
+remote: ========================================================================
+remote: 
+`
+	expectedReformat := "remote: This deploy key does not have write access to this project."
+
+	err := errors.New(gitlabMessage)
+	err = libgit2PushError(err)
+	reformattedMessage := err.Error()
+	if reformattedMessage != expectedReformat {
+		t.Errorf("expected %q, got %q", expectedReformat, reformattedMessage)
+	}
+}
+
+func TestLibgit2Multiline(t *testing.T) {
+	// this is a hypothetical error message, in which the useful
+	// content spans more than one line
+	multilineMessage := `remote: 
+remote: ========================================================================
+remote: 
+remote: This deploy key does not have write access to this project.
+remote: You will need to create a new deploy key.
+remote: 
+remote: ========================================================================
+remote: 
+`
+	expectedReformat := "remote: This deploy key does not have write access to this project. You will need to create a new deploy key."
+
+	err := errors.New(multilineMessage)
+	err = libgit2PushError(err)
+	reformattedMessage := err.Error()
+	if reformattedMessage != expectedReformat {
+		t.Errorf("expected %q, got %q", expectedReformat, reformattedMessage)
+	}
+}
+
+func TestLibgit2ErrorUnchanged(t *testing.T) {
+	// this is (roughly) what GitHub sends if the deploy key doesn't have write access
+	regularMessage := `remote: ERROR: deploy key does not have permissions`
+	expectedReformat := regularMessage
+	err := errors.New(regularMessage)
+	err = libgit2PushError(err)
+	reformattedMessage := err.Error()
+	if reformattedMessage != expectedReformat {
+		t.Errorf("expected %q, got %q", expectedReformat, reformattedMessage)
+	}
+}
+
+func TestGoGitErrorReplace(t *testing.T) {
+	// this is what go-git uses as the error message is if the remote
+	// sends a blank first line
+	unknownMessage := `unknown error: remote: `
+	err := errors.New(unknownMessage)
+	err = gogitPushError(err)
+	reformattedMessage := err.Error()
+	if reformattedMessage == unknownMessage {
+		t.Errorf("expected rewritten error, got %q", reformattedMessage)
+	}
+}
+
+func TestGoGitErrorUnchanged(t *testing.T) {
+	// this is (roughly) what GitHub sends if the deploy key doesn't
+	// have write access; go-git passes this on verbatim
+	regularMessage := `remote: ERROR: deploy key does not have write access`
+	expectedReformat := regularMessage
+	err := errors.New(regularMessage)
+	err = gogitPushError(err)
+	reformattedMessage := err.Error()
+	// test that it's been rewritten, without checking the exact content
+	if len(reformattedMessage) > len(expectedReformat) {
+		t.Errorf("expected %q, got %q", expectedReformat, reformattedMessage)
+	}
+}