Add customisable userSettings

userSettings can now be passed in on initialization via
`helper.init(runtimepath, userSettings)` as well as during the runtime
using `helper.settings(userSettings)`.

This makes it easier for unit tests to emulate their production
environment.

Fixes #21

README.md

@@ -104,6 +104,14 @@ We then have a set of mocha unit tests.  These tests check that the node loads c
 
 To get started, we need to tell the helper where to find the node-red runtime.  this is done by calling `helper.init(require.resolve('node-red'))` as shown.
 
+The helper takes an optional `userSettings` parameter which is merged with the runtime defaults.
+
+```javascript
+helper.init(require.resolve('node-red'), { 
+    functionGlobalContext: { os:require('os') }
+});
+```
+
 ## Getting nodes in the runtime
 
 The asynchronous `helper.load()` method calls the supplied callback function once the Node-RED server and runtime is ready.  We can then call the `helper.getNode(id)` method to get a reference to nodes in the runtime.  For more information on these methods see the API section below.
@@ -320,6 +328,20 @@ Example:
 helper.request().post('/inject/invalid').expect(404).end(done);
 ```
 
+### settings(userSettings)
+
+Merges any userSettings with the defaults returned by `RED.settings`. Each invocation of this method will overwrite the previous userSettings to prevent unexpected problems in your tests.
+
+This will enable you to replicate your production environment within your tests, for example where you're using the `functionGlobalContext` to enable extra node modules within your functions.
+
+```javascript
+// functions can now access os via global.get('os')
+helper.settings({ functionGlobalContext: { os:require('os') } });
+
+// reset back to defaults
+helper.settings({ });
+```
+
 ### startServer(done)
 
 Starts a Node-RED server for testing nodes that depend on http or web sockets endpoints like the debug node.
@@ -361,4 +383,4 @@ var logEvents = helper.log().args.filter(function(evt {
 
     npm run examples
 
-This runs tests on an included lower-case node (as above) as well as snaphots of some of the core nodes' Javascript files to ensure the helper is working as expected.
+This runs tests on an included lower-case node (as above) as well as snaphots of some of the core nodes' Javascript files to ensure the helper is working as expected.

examples/function_spec.js

@@ -197,6 +197,28 @@ describe('function node', function() {
         });
     });
 
+    it('should access functionGlobalContext set via herlp settings()', function(done) {
+        var flow = [{id:"n1",type:"function",wires:[["n2"]],func:"msg.payload=global.get('foo');return msg;"},
+                    {id:"n2", type:"helper"}];
+        helper.settings({
+            functionGlobalContext: {
+                foo: (function() {
+                    return 'bar';
+                })(),
+            },
+        });
+        helper.load(functionNode, flow, function() {
+            var n1 = helper.getNode("n1");
+            var n2 = helper.getNode("n2");
+            n2.on("input", function(msg) {
+                msg.should.have.property('payload', 'bar');
+                done();
+            });
+            n1.receive({payload:"replaceme"});
+        });
+        helper.settings({});
+    });
+
     function testNonObjectMessage(functionText,done) {
         var flow = [{id:"n1",type:"function",wires:[["n2"]],func:functionText},
                 {id:"n2", type:"helper"}];

index.js

@@ -128,11 +128,35 @@ class NodeTestHelper extends EventEmitter {
         }
     }
 
-    init(runtimePath) {
+    init(runtimePath, userSettings) {
         runtimePath = runtimePath || findRuntimePath();
         if (runtimePath) {
             this._initRuntime(runtimePath);
+            if (userSettings) {
+                this.settings(userSettings);
+            }
+        }
+    }
+
+    /**
+     * Merges any userSettings with the defaults returned by `RED.settings`. Each
+     * invocation of this method will overwrite the previous userSettings to prevent
+     * unexpected problems in your tests.
+     *
+     * This will enable you to replicate your production environment within your tests,
+     * for example where you're using the `functionGlobalContext` to enable extra node
+     * modules within your functions.
+     * @example
+     * helper.settings({ functionGlobalContext: { os:require('os') } });
+     * @param {Object} userSettings - an object containing the runtime settings
+     * @return {Object} custom userSettings merged with default RED.settings
+     */
+    settings(userSettings) {
+        if (userSettings) {
+            // to prevent unexpected problems, always merge with the default RED.settings
+            this._settings = Object.assign({}, this._RED.settings, userSettings);
         }
+        return this._settings;
     }
 
     load(testNode, testFlow, testCredentials, cb) {

test/settings_spec.js

@@ -0,0 +1,28 @@
+var should = require("should");
+var NodeTestHelper = require('../index.js').NodeTestHelper;
+
+var helper;
+beforeEach(function() {
+    // .init() is implicitly called on instantiation so not required
+    helper = new NodeTestHelper();
+});
+
+describe('add custom settings on init', function () {
+  it('should merge custom settings with RED.settings defaults', function () {
+    helper._settings.should.not.have.property('functionGlobalContext');
+    helper.init(null, {functionGlobalContext: {}});
+    helper._settings.should.have.property('functionGlobalContext');
+  });
+});
+
+describe('helper.settings() usage', function() {
+  it('should return a settings Object', function() {
+      var settings = helper.settings();
+      should.exist(settings);
+      settings.should.have.property('get');
+  });
+  it('should not maintain settings state across multiple invocations', function() {
+      helper.settings({ foo: true }).should.have.property('foo');
+      helper.settings({ bar: true }).should.not.have.property('foo');
+  });
+});