Add Running Tests through Stoplight article (#152)

* Add first version of Running Tests with Stoplight article.

* Add callouts

* Update run-test-stoplight.md

* Updates

* Add spacing to bullets

articles/testing/run-test-stoplight.md

@@ -1 +1,70 @@
+# Running Scenarios
 
+Scenarios allow you to quickly and efficiently test APIs. Scenarios can be
+run in a variety of different ways, including from the [command-line with
+Prism](./run-test-terminal.md) or by [URL](./run-test-url). However, the easiest
+way is through the Stoplight editor.
+
+<!-- theme: info -->
+
+> If you haven't created your first scenario yet, please [do so before
+> continuing](./scenarios-introduction.md)
+
+Scenarios in Stoplight are composed of three different levels:
+
+* **Steps**: low-level building blocks that compose a scenario.
+  Steps allow you to easily chain individual actions (e.g., performing a
+  web request) together, enabling for more complex testing workflows.
+
+* **Scenarios**: a series of **steps** that perform a high-level
+  action (e.g., registering a new user).
+
+* **Collections**: a series of **scenarios** that encapsulate an
+  entire test suite. Collections are the highest-level building blocks for creating
+  a library of API interactions and tests.
+
+Each level above can be run individually or all together.
+
+## Running a Step
+
+Once you have created a scenario **step**, use the **Run Step** button to
+execute that step. The **Run Step** button is available towards the top of the
+editor, as shown below.
+
+![](../../assets/images/run-test-stoplight.png)
+
+## Running a Scenario
+
+Once you have added enough steps to a **scenario**, use the **Run Scenario**
+button to execute that scenario. The **Run Scenario** button is available
+towards the top of the editor while viewing the scenario configuration/overview,
+as show below.
+
+![](../../assets/images/run-test-stoplight2.png)
+
+<!-- theme: info -->
+
+> Scenarios can also be run directly from every step using the **Run Scenario**
+> button
+
+## Running a Collection
+
+Once you have added created enough scenarios to compose a **collection**, use
+the **Run Collection** button to run the entire collection (including all
+scenarios and steps). The **Run Collection** button is available towards the top
+of the editor while viewing the collection home screen, as shown below.
+
+![](../../assets/images/run-test-stoplight3.png)
+
+<!-- theme: info -->
+
+> Collections can also be run from the scenario and step screens using the **Run
+> Collection** button
+
+---
+
+**Related**
+
+* [Scenarios Overview](./scenarios-introduction.md)
+* [Running Scenarios from the Command-Line](./run-test-terminal.md)
+* [Running Scenarios by URL](./run-test-url.md)