doc: add e2e test (#21)

src/SUMMARY.md

@@ -11,6 +11,7 @@
     - [Prerequisites](./building/prerequisites.md)
     - [Suggested Workflows](./building/suggested.md)
 - [Testing](./testing/intro.md)
+    - [E2E](./testing/e2e.md)
 - [Debugging](./debugging/intro.md)
 - [Profiling](./profiling/intro.md)
 - [Releasing](./releasing/intro.md)

src/testing/e2e.md

@@ -0,0 +1,79 @@
+# E2E
+
+The `packages/playground` provides e2e testing feature. We use [playwright](https://github.com/Microsoft/playwright) as the e2e testing framework.
+
+## Cases
+
+The entry point of a test case is a file ending with `.test.ts`, and the parent directory of this file is the project directory.
+
+Here are some rules about test cases:
+
+* The project directory must contain `rspack.config.js` to start the dev server.
+* The project directory can contain multi `*.test.ts`.
+* All test cases share dependencies, so just add dependencies in `packages/playground/package.json`.
+* The cases folder should contain the category folders and then is the project folders. In principle, there should be no third-level directory.
+
+## Fixtures
+
+The `fixtures` is a feature of playwright, in short it provides a variable that is generated in before{Each|All} and destroyed in after{Each|All}. More information see [test-fixtures](https://playwright.dev/docs/test-fixtures)
+
+Here are some rules when defining a new fixture:
+
+* Private fixtures should start with `_` and are used only in the current file.
+* A file only provides fixtures with the same name.
+* A file can only provide one option and starts with `default`
+* Register fixtures in `fixtures/index.ts` and export only necessary variables and types.
+
+Here are some existing fixtures:
+
+#### pathInfo
+
+This fixture will generate test environment, and calculate the PathInfo.
+``` ts
+type PathInfo = {
+    // test file path
+    testFile: string;
+    // project dir
+    testProjectDir: string
+    // temporary project directory to be copied into
+    tempProjectDir: string
+}
+```
+
+#### rspack
+
+This fixture will start the rspack dev server and provide some useful methods.
+``` ts
+type Rspack = {
+    // rspack running project directory
+    projectDir: string
+    // rspack compiler
+    compiler: Compiler
+    // rspack dev server
+    devServer: DevServer
+    // waiting for rspack build finish
+    waitingForBuild: () => Promise<void>
+    // waiting for hmr finish, the poll function is used to check
+    waitingForHmr: (poll: () => Promise<boolean>) => Promise<void>
+}
+```
+
+#### fileAction
+
+This fixture will provide file change operations.
+``` ts
+type fileAction = {
+    updateFile(relativePath: string, fn: (content: string) => string): void
+    deleteFile(relativePath: string): void
+}
+```
+
+## How it works
+
+* playwright scan all test case and allocates a worker to run each case.
+* `pathInfo` copy the project directory corresponding to the current case to `temp/${worker_index}`.
+* `rspack` rewrite dev server port to `8000 + worker_index` and start compiler and dev server in `temp/${worker_index}`.
+* run current tests.
+* `rspack` close dev server and compiler.
+* `pathInfo` clear `temp/${worker_index}`
+