docs: Add documentation regarding raven-teskit plugin (#1231)

* handle case where both stackstraces are undefined when checking 'isSameException'
* add documentation regarding raven-teskit plugin
* adding raven-testkit docs to Tips and Tricks

Author: zivl

docs/tips.rst

@@ -182,3 +182,49 @@ and will fail on slow connection or long response time:
         dataType: 'script',
         crossDomain: true
     });
+
+
+Raven Test Kit
+--------------
+When building tests for your application, you want to assert that the right flow-tracking or error is being sent to *Sentry*,
+**but** without really sending it to the *Sentry* system.
+This way you won't swamp it with false reports during test running and other CI operations.
+
+`Raven Test Kit <https://github.com/wix/raven-testkit>`_ enables Raven to work natively in your application,
+but it overrides the default Raven transport mechanism so the report is not really sent but rather logged locally.
+In this way, the logged reports can be fetched later for usage verification or other uses you may have in your testing environment.
+
+Installation
+````````````
+.. code-block:: sh
+
+  $ npm install raven-testkit --save-dev
+
+How to Use
+``````````
+Then you may create a ``testkit`` instance and validate your reports against it as follows:
+
+.. code:: javascript
+
+  import testKitInitializer from 'raven-testkit'
+
+  const testKit = testKitInitializer(Raven)
+
+  // any scenario that should call Raven.catchException(...)
+
+  expect(testKit.reports()).to.have.lengthOf(1)
+  const report = testKit.reports()[0]
+  expect(report).to.have.property('release').to.equal('test')
+
+
+Additionally, you may pass your own ``shouldSendCallback`` logic
+
+.. code:: javascript
+
+  const shouldSendCallback = data => {
+      return /* your own logic */
+  }
+  const testKit = testKitInitializer(Raven, shouldSendCallback)
+
+
+Other useful API, more example usage and updates can be found in `Raven Test Kit <https://github.com/wix/raven-testkit>`_