Mocha runner reports killed by: undefined when a hook fails.

[nicojs]

Summary

When a before each hook fails, the test that gets reported failed is not actually a test, but the name of the hook.

For example: DirectoryRequireCache "before each" hook for "should clear recorded files" instead of DirectoryRequireCache should clear recorded files

Stryker config

{
  "testRunner": "mocha"
}

Stryker environment

+-- @stryker-mutator/core@4.4.0
+-- @stryker-mutator/mocha-runner@4.4.0