Mocha 7.0.1 quits watching when all tests file are removed

[normanzb]

Prerequisites

• [x ] Checked that your issue hasn't already been filed by cross-referencing issues with the faq label
• [ x] 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.
• [x ] '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
• [x ] 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

Mocha 7 quits watching process when the test folder is deleted

Steps to Reproduce

1. Install mocha 7.0.1 npm i mocha@7.0.1 -D
2. Create a simple test file in "test" folder
3. Start mocha in watching mode: ./node_modules/.bin/mocha --watch
4. In another terminal window, remove "test" folder: rm -r test

test.js file:

describe("test",() => {
  it('logs', ()=>{console.log(1)})
})

Expected behavior: [What you expect to happen] Mocha continues to watching newly added files if any, mocha doesn't quit the process.

Actual behavior: [What actually happens]

Mocha 7 quits with error message: "Error: No test files found: "test"" This is not an issue in mocha@6.

Reproduces how often: [What percentage of the time does it reproduce?] 100%

Versions

• The output of mocha --version and node node_modules/.bin/mocha --version: 7.0.1
• The output of node --version: v13.3.0
• Your operating system
  • name and version: macOS 10.13.6 (17G5019)
  • architecture (32 or 64-bit): 64
• Your shell (e.g., bash, zsh, PowerShell, cmd): bash
• Your browser and version (if running browser tests): none
• Any third-party Mocha-related modules (and their versions): none
• Any code transpiler (e.g., TypeScript, CoffeeScript, Babel) being used (and its version): none

Additional Information

[craigtaub]

Is there a scenario where it is useful for mocha to continue watching here rather than quit? A lot has changed since v6 and the expected behaviour when no test files are found is to exit the current process, regardless of watch mode.

[JoshuaKGoldberg]

🤔 I can see an argument that Mocha being run in watch mode is an indication it's meant as a long-lived development utility. As in, you might start it, then write your tests.

cc @mochajs/maintenance-crew - I think we can consider this a bug and accepting PRs. What do you think?