docs

docs/index.md

@@ -899,6 +899,10 @@ To ensure your tests aren't leaving messes around, here are some ideas to get st
 - Try something like [wtfnode][npm-wtfnode]
 - Use [`.only`](#exclusive-tests) until you find the test that causes Mocha to hang
 
+### `--fail-zero`
+
+> _New in v9.1.0._ Fail test run if no tests are encountered with `exit-code` 1.
+
 ### `--forbid-only`
 
 Enforce a rule that tests may not be exclusive (use of e.g., `describe.only()` or `it.only()` is disallowed).
@@ -2118,6 +2122,7 @@ mocha.setup({
   bail: true,
   checkLeaks: true,
   dryRun: true,
+  failZero: true,
   forbidOnly: true,
   forbidPending: true,
   global: ['MyLib'],