diff --git a/lib/core/serializer/url-serializer.test.ts b/lib/core/serializer/url-serializer.test.ts
new file mode 100644
index 0000000..ce8d6dd
--- /dev/null
+++ b/lib/core/serializer/url-serializer.test.ts
@@ -0,0 +1,75 @@
+import { describe, expect, it, vi } from 'vitest'
+import { parseUrl } from './url-serializer'
+
+const dummyQueryParser = (s: string) => ({ raw: s })
+
+describe('parseUrl', () => {
+  it('parses a full absolute URL', () => {
+    const result = parseUrl({
+      str: 'https://example.com:8080/foo/bar?x=1#frag',
+      parseQuery: dummyQueryParser,
+    })
+
+    expect(result).toEqual({
+      protocol: 'https',
+      hostname: 'example.com',
+      paths: ['foo', 'bar'],
+      port: 8080,
+      fragment: 'frag',
+      queries: { raw: '?x=1' },
+    })
+  })
+
+  it('parses a relative path without protocol or hostname', () => {
+    const result = parseUrl({
+      str: '/some/path',
+      parseQuery: dummyQueryParser,
+    })
+
+    expect(result).toEqual({
+      paths: ['some', 'path'],
+      queries: Object.create(null),
+    })
+  })
+
+  it('parses relative slash-only path with query and fragment', () => {
+    const parser = vi.fn(dummyQueryParser)
+    const result = parseUrl({
+      str: '/?a=1#b',
+      parseQuery: parser,
+    })
+
+    expect(result.paths).toEqual([])
+    expect(result.queries).toEqual({ raw: '?a=1' })
+    expect(parser).toHaveBeenCalledOnce()
+  })
+
+  it('parses protocol-relative URL (//host/...)', () => {
+    const result = parseUrl({
+      str: '//foo.com/bar',
+      parseQuery: dummyQueryParser,
+    })
+
+    expect(result).toEqual({
+      hostname: 'foo.com',
+      paths: ['bar'],
+      queries: Object.create(null),
+    })
+  })
+
+  it('throws if the string is not a valid URL', () => {
+    expect(() =>
+      parseUrl({ str: 'not a url', parseQuery: dummyQueryParser }),
+    ).toThrowError('Invalid URL')
+  })
+
+  it('omits protocol and hostname when not applicable', () => {
+    const r1 = parseUrl({ str: '/', parseQuery: dummyQueryParser })
+    expect(r1.protocol).toBeUndefined()
+    expect(r1.hostname).toBeUndefined()
+
+    const r2 = parseUrl({ str: '//host', parseQuery: dummyQueryParser })
+    expect(r2.protocol).toBeUndefined()
+    expect(r2.hostname).toBe('host')
+  })
+})