Pass local context to browser.debug() command. (#4299)

* Allow local context to be passed to browser.debug command.

* Improve debug experience.

lib/api/client-commands/debug.js

@@ -1,6 +1,7 @@
 const EventEmitter = require('events');
 const NightwatchRepl = require('../../testsuite/repl');
 const Debuggability = require('../../utils/debuggability.js');
+const {By} = require('selenium-webdriver');
 
 /**
  * This command halts the test execution and provides users with a REPL interface where they can type
@@ -37,24 +38,37 @@ class Debug extends EventEmitter {
   }
 
   command(config, callback) {
+    // Create context for vm
+    const context = {
+      browser: this.api,
+      app: this.api,
+      by: By,
+      By: By
+    };
+
+    // set the user provided context
+    if (config.context) {
+      Object.assign(context, config.context);
+      delete config.context;
+    }
+
     const repl = new NightwatchRepl(config);
 
     // eslint-disable-next-line
     console.log(NightwatchRepl.introMessage());
 
-    // Create context for vm
-    const context = {
-      browser: this.api,
-      app: this.api
-    };
+    // TODO: what's the use of this `if` block?
     if (config?.selector) {
       this.api.executeScript('console.log("Element ' + config.selector + ':", document.querySelector("' + config.selector + '"))');
     }
+
     // Before starting REPL server, Set debugMode to true
     Debuggability.debugMode = true;
+
     // Set isES6AsyncTestcase to true in debugmode
     const isES6AsyncTestcase = this.client.isES6AsyncTestcase;
     this.client.isES6AsyncTestcase = true;
+
     repl.startServer(context);
 
     repl.onExit(() => {

lib/testsuite/repl.js

@@ -62,7 +62,7 @@ module.exports = class NightwatchRepl {
   }
 
   async _handleResult(result, callback) {
-    const resultIsPromise = result instanceof Promise;
+    const resultIsPromise = result instanceof Promise || (result && typeof result.then === 'function');
 
     if (!resultIsPromise) {
       return callback(null, result);