fix style content url normalizer and add some tests

test/snapshot.test.ts

@@ -0,0 +1,31 @@
+import 'mocha';
+import { expect } from 'chai';
+import { absoluteToStylesheet } from '../src/snapshot';
+
+describe('absolute url to stylesheet', () => {
+  const href = 'http://localhost/css/style.css';
+
+  it('can handle same level path', () => {
+    expect(absoluteToStylesheet('url("./a.jpg")', href)).to.equal(
+      `url('http://localhost/css/a.jpg')`,
+    );
+  });
+
+  it('can handle parent level path', () => {
+    expect(absoluteToStylesheet('url("../a.jpg")', href)).to.equal(
+      `url('http://localhost/a.jpg')`,
+    );
+  });
+
+  it('can handle absolute path', () => {
+    expect(absoluteToStylesheet('url("/a.jpg")', href)).to.equal(
+      `url('http://localhost/a.jpg')`,
+    );
+  });
+
+  it('can handle external path', () => {
+    expect(
+      absoluteToStylesheet('url("http://localhost/a.jpg")', href),
+    ).to.equal(`url('http://localhost/a.jpg')`);
+  });
+});