Regression: Mocha ignores files after `--` (end of CLI options)

[demurgos]

Prerequisites

• Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• Checked next-gen ES issues and syntax problems by using the same environment and/or transpiler configuration without Mocha to ensure it isn't just a feature that actually isn't supported in the environment in question or a bug in your code.
• 'Smoke tested' the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, your usage of Mocha, or Mocha itself
• Ensured that there is no discrepancy between the locally and globally installed versions of Mocha. You can find them with: node node_modules/.bin/mocha --version(Local) and mocha --version(Global). We recommend that you not install Mocha globally.

Description

During the Mocha@6 rewrite of the CLI, a regression occurred: Mocha now ignores the test files supplied after --. Support for -- is required to allow consumers to safely generate the command line arguments and avoid conflicts between test files and CLI options.

Steps to Reproduce

In a directory with test.spec.js, run:

mocha -- test.spec.js

Expected behavior: Mocha executes the tests in test.spec.js.

Actual behavior: Mocha immediately returns with the following error:

Error: No test files found: "test"

Reproduces how often: All the time

Versions

• The output of mocha --version and node node_modules/.bin/mocha --version: 6.1.4
• The output of node --version: 12.1.0
• Your operating system
  • name and version: Linux 5.0.9
  • architecture (32 or 64-bit): 64-bit
• Your shell (e.g., bash, zsh, PowerShell, cmd): Bash
• Your browser and version (if running browser tests): N/A
• Any third-party Mocha-related modules (and their versions): N/A
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version): N/A

Additional Information

In Mocha@5, the command mocha -- test.spec.js works. It fails since the rewrite from #3556.

[plroebuck]

Not sure we ever "officially" said "--" was supported...

Assuming so, our support of it is "borken" in couple aspects:

1. Added to wrong end of cmdline arguments (see mocha:cli:mocha exec _mocha)
2. Incorrectly strips first dash from "--" and creates "-" option, assigning positional argument to it
   (see mocha:cli:run post-yargs)

[jimthedev]

Looks like v13.1.1 has the referenced issue fixed even if it hasn't been closed. There is a linked PR.