v8.takeCoverage()方法允许用户按需将 NODE_V8_COVERAGE 开始的覆盖写入磁盘。

The v8.takeCoverage() method allows the user to write the coverage started by NODE_V8_COVERAGE to disk on demand. This method can be invoked multiple times during the lifetime of the process, each time the execution counter will be reset and a new coverage report will be written to the directory specified by NODE_V8_COVERAGE.

When the process is about to exit, one last coverage will still be written to disk, unless v8.stopCoverage() is invoked before the process exits.