ensure --debug becomes --inspect; closes #3697

- add some handiness to the integration test helpers
- update docstrings in integration test helpers

bin/mocha

@@ -58,6 +58,28 @@ Object.keys(opts).forEach(opt => {
   }
 });
 
+// allow --debug to invoke --inspect on Node.js v8 or newer
+if (childOpts.debug) {
+  nodeOpts.inspect = childOpts.debug;
+  childOpts.timeout = false;
+  delete childOpts.debug;
+  debug('--debug -> --inspect');
+} else if (childOpts['debug-brk']) {
+  nodeOpts['inspect-brk'] = childOpts['debug-brk'];
+  childOpts.timeout = false;
+  delete childOpts['debug-brk'];
+  debug('--debug-brk -> --inspect-brk');
+}
+
+// historical
+if (nodeOpts.gc) {
+  deprecate(
+    '"-gc" is deprecated and will be removed from a future version of Mocha.  Use "--gc-global" instead.'
+  );
+  nodeOpts['gc-global'] = nodeOpts.gc;
+  delete nodeOpts.gc;
+}
+
 // Native debugger handling
 // see https://nodejs.org/api/debugger.html#debugger_debugger
 // look for 'debug' or 'inspect' that would launch this debugger,