tests: Make test-js-with-node handling smarter.

Added support for passing a filename without `.js` suffix.
This then fixed the issue of no complaints for invalid test
files. Now, throws an error for invalid test files.

Fixes #8579.

frontend_tests/zjsunit/finder.js

@@ -33,7 +33,7 @@ exports.find_files_to_run = function () {
     }
 
     testsDifference.forEach(function (filename) {
-        console.log(filename + " does not exist");
+        throw (filename + ".js does not exist");
     });
 
     tests.sort();

tools/test-js-with-node

@@ -93,6 +93,12 @@ os.environ['TZ'] = 'UTC'
 
 INDEX_JS = 'frontend_tests/zjsunit/index.js'
 
+# Add ".js" to the end of all the file arguments, so index.js
+# can actually verify if the file exists or not.
+for index, arg in enumerate(options.args):
+    if not arg.endswith('.js'):
+        options.args[index] = arg + '.js'
+
 # The index.js test runner is the real "driver" here, and we launch
 # with either istanbul or node, depending on whether we want coverage
 # reports.  Running under istanbul is slower and creates funny