v8.takeCoverage()

v8.takeCoverage() 方法允许用户按需将 NODE_V8_COVERAGE 开始的覆盖率写入磁盘。该方法可以在进程生命周期内多次调用。每次调用时，执行计数器都会被重置，一个新的覆盖率报告将被写入 NODE_V8_COVERAGE 指定的目录。

【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.】

当进程即将退出时，除非在进程退出前调用 v8.stopCoverage()，否则最后一次覆盖率仍会写入磁盘。

【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.】