fix: if filtering by grep eliminates all specs, do not filter them

Author: bahmutov

README.md

@@ -205,6 +205,8 @@ Note: this requires installing this plugin in your project's plugin file, see th
 
 Note 2: the `grepFilterSpecs` option is only compatible with the positive `grep` and `grepTags` options, not with the negative "!..." filter.
 
+Note 3: if there are no files remaining after filtering, the plugin prints a warning and leaves all files unchanged to avoid the test runner erroring with "No specs found".
+
 **Tip:** you can set this environment variable in the `cypress.json` file to enable it by default and skip using the environment variable:
 
 ```json

src/plugin.js

@@ -117,7 +117,13 @@ function cypressGrepPlugin(config) {
       debug('found "%s" in %d specs', grep, specsWithText.length)
       debug('%o', specsWithText)
 
-      config.testFiles = specsWithText
+      if (specsWithText.length) {
+        config.testFiles = specsWithText
+      } else {
+        // hmm, we filtered out all specs, probably something is wrong
+        console.warn('Grep "%s" has eliminated all specs', grep)
+        console.warn('Will leave all specs to run to filter at run-time')
+      }
     }
   }