Add spec documentation

docs/writing-specs.md

@@ -0,0 +1,61 @@
+# Writting specs
+
+Atom uses [Jasmine](http://jasmine.github.io/2.0/introduction.html) as its spec framework. Any new functionality should have specs to guard against regressions.
+
+## Create a new spec
+
+[Atom specs](https://github.com/atom/atom/tree/master/spec) and [package specs](https://github.com/atom/markdown-preview/tree/master/spec) are added to their respective `spec` directory. The example below creates a spec for Atom core.
+
+0. Create a spec file
+
+  Spec files **must** end with `-spec` so add `sample-spec.coffee` to `atom/spec`.
+
+0. Add one or more `describe` method
+
+  The `describe` method takes two arguments, a description and a function. If the description explains a behavior it typically begins with `when` if it is more like a unit test it begins with the method name.
+
+  ```coffee
+  describe "when a test is written", ->
+    # contents
+  ```
+
+  or
+
+  ```coffee
+  describe "Editor::moveUp", ->
+    # contents
+  ```
+
+0. Add one or more `it` method
+
+  The `it` method also takes two arugments, a description and a function. Try and make the description flow with the `it` method. For example, a description of `this should work` doesn't read well as `it this should work`. But a description of `should work` sounds great as `it should work`.
+
+  ```coffee
+  describe "when a test is written", ->
+    it "has some expectations that should pass", ->
+      # Expectations
+  ```
+
+0. Add one or more expectations
+
+  The best way to learn about expectations is to read the [jamsine documentation](http://jasmine.github.io/2.0/introduction.html#section-Expectations) about them. Below is a simple example.
+
+  ```coffee
+  describe "when a test is written", ->
+    it "has some expectations that should pass", ->
+      expect("apples").toEqual("apples")
+      expect("oranges").not.toEqual("apples")
+  ```
+
+## Runnings specs
+
+Most of the time you'll want to run specs by triggering the `window:run-package-specs` command. This command is not only to run package specs, it is also for Atom core specs. This will run all the specs in the current project's spec directory. If you want to run the Atom core specs and **all** the default package specs trigger the `window:run-all-specs` command.
+
+To run a limited subset of specs use the `fdescribe` or `fit` methods. You can use those to focus a single spec or several specs. In the example above, focusing an individual spec looks like this:
+
+```coffee
+describe "when a test is written", ->
+  fit "has some expectations that should pass", ->
+    expect("apples").toEqual("apples")
+    expect("oranges").not.toEqual("apples")
+```