Provide helpers and tests for common error types

Unify error handling in apiserver into a single path - RESTStorage
objects must provide appropriate errors individually.  Ensure ALL
errors which can be traced to logical faults with RESTStorage are
returned as api.Status objects.

pkg/apiserver/errors_test.go

@@ -0,0 +1,42 @@
+/*
+Copyright 2014 Google Inc. All rights reserved.
+
+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 apiserver
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestErrorNew(t *testing.T) {
+	err := NewAlreadyExistsErr("test", "1")
+	if !IsAlreadyExists(err) {
+		t.Errorf("expected to be already_exists")
+	}
+	if IsConflict(err) {
+		t.Errorf("expected to not be confict")
+	}
+	if IsNotFound(err) {
+		t.Errorf("expected to not be not_found")
+	}
+
+	if !IsConflict(NewConflictErr("test", "2", errors.New("message"))) {
+		t.Errorf("expected to be confict")
+	}
+	if !IsNotFound(NewNotFoundErr("test", "3")) {
+		t.Errorf("expected to be not found")
+	}
+}