Improve the server assets cache invalidation logic

Fixes #6199

resources/resource_cache_test.go

@@ -0,0 +1,58 @@
+// Copyright 2019 The Hugo Authors. 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 resources
+
+import (
+	"path/filepath"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestResourceKeyPartitions(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		input    string
+		expected []string
+	}{
+		{"a.js", []string{"js"}},
+		{"a.scss", []string{"sass", "scss"}},
+		{"a.sass", []string{"sass", "scss"}},
+		{"d/a.js", []string{"d", "js"}},
+		{"js/a.js", []string{"js"}},
+		{"D/a.JS", []string{"d", "js"}},
+		{"d/a", []string{"d"}},
+		{filepath.FromSlash("/d/a.js"), []string{"d", "js"}},
+		{filepath.FromSlash("/d/e/a.js"), []string{"d", "js"}},
+	} {
+		c.Assert(ResourceKeyPartitions(test.input), qt.DeepEquals, test.expected, qt.Commentf(test.input))
+	}
+}
+
+func TestResourceKeyContainsAny(t *testing.T) {
+	c := qt.New(t)
+
+	for _, test := range []struct {
+		key      string
+		filename string
+		expected bool
+	}{
+		{"styles/css", "asdf.css", true},
+		{"styles/css", "styles/asdf.scss", true},
+		{"js/foo.bar", "asdf.css", false},
+	} {
+		c.Assert(ResourceKeyContainsAny(test.key, ResourceKeyPartitions(test.filename)), qt.Equals, test.expected)
+	}
+}