Unexpected Indentation Level in Tests

As mentioned in #950, the tests produce a strange behavior with indentation of PHP code blocks in markdown.

Even when no tabWidth is configured in the markdown test (currently it is set to 4 to work around this issue), PHP code is indented by 2 spaces with the standalone build:

[...]

```php
function test(){$a=1;}
`​``

[...]

becomes

[...]

```php
function test()
{
  $a = 1;
}
`​``

[...]

Note: Be careful when copy-pasting the code above. The code fences contain zero-width spaces to retain syntax highlighting.

This incorrect behavior is pretty unique:

• It does not occur in the same test for the Node.js build, which correctly indents by 4 spaces in the tests.

• It does not occur in the standalone build when used in the browser.

• It does not even occur in the test for the standalone build, when the jest.config.js is changed to not using projects (which it currently does), to something like this:

  module.exports = {
    setupFiles: ["<rootDir>/tests_config/run_spec.js"],
    testRegex: "jsfmt\\.spec\\.js$|__tests__/.*\\.js$",
    snapshotSerializers: ["jest-snapshot-serializer-raw"],
    testEnvironment: "jsdom",
    globals: {
      STANDALONE: true
    }
  };
  

So especially because of the last point, I'm assuming this has something to do with the architecture of the tests. I wasn't able to narrow it down any further.

As mentioned above, currently there's a workaround (introduced in #950) to not break the tests with something that doesn't occur "in the wild", but it should probably be taken a deeper look on.

从 tests/markdown 下的 markdown 测试开始，并比较 Node.js 和 standalone 的结果。检查 jest.config.js，尤其是其中的 projects 配置，并使用 tests_config/run_spec.js 重现差异。当 standalone 测试不再需要 tabWidth: 4 这一变通方案，并且与预期的缩进一致时，即表示完成。