Add contributing docs

Reviewed By: danielbuechele

Differential Revision: D6976258

fbshipit-source-id: 71b3d0ab4a071ce0c4a9c1241cd6295aa6d52b8e

website/contents/contributing/adding-a-test.md

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----
-path: "contributing/adding-a-test"
-title: "Adding a Test"
-hasPlayground: false
----
-
-## Adding a Test

website/contents/contributing/checking-out-the-code.md

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-path: "contributing/checking-out-the-code"
-title: "Checking Out the Code"
-hasPlayground: false
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-
-## Checking Out the Code

website/contents/contributing/making-a-change.md

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-path: "contributing/making-a-change"
-title: "Making a change"
-hasPlayground: false
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-
-## Making a change

website/contents/contributing/opening-a-pull-request.md

@@ -4,4 +4,52 @@ title: "Opening a Pull Request"
 hasPlayground: false
 ---
 
-## Opening a Pull Request
+# Opening a Pull Request
+
+Before opening your first pull request to Yoga you have to know how to get the code,
+install build time dependencies, and test the code locally.
+
+### Clone
+
+```
+$> git clone https://github.com/facebook/yoga.git
+$> cd yoga
+```
+
+### Install dependencies
+
+```
+$> git submodule init
+$> git submodule update
+$> brew install buck
+```
+
+### Build and Test
+
+```
+$> buck build //:yoga
+$> buck test //:yoga
+```
+
+## Making a Change
+
+Now all you need to do is make your change and test it before submitting a pull request for review.
+Below is the general structure of the repo and where you may want to make your change. One you have
+made your change see the [testing documentation](/contributing/testing) for more on how to test your change.
+
+``` bash
+/yoga
+|-- yoga                  # Home to the main Yoga codebase written in C++. Any algorithmic changes should be made here
+|-- lib                   # Yoga external dependencies. Be thoughtful adding any new ones
+|-- tests                 # Yoga's C++ test suite. Both manaul and generated tests
+|-- gentest
+|   |-- fixtures          # html fixtures for generated tests    
+|-- java         
+|   |-- com/facebook/yoga # Java binding code
+|   |-- jni               # JNI binding code
+|-- yogacore              # Android bindings without View support
+|-- android               # Android View bindings
+|-- YogaKit               # iOS UIView bindings
+|-- javascript            # emscripten / javascript bindings
+|-- csharp                # .NET bindings in c#
+```

website/contents/contributing/running-the-test-suite.md

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-path: "contributing/running-the-test-suite"
-title: "Running the Test Suite"
-hasPlayground: false
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-
-## Running the Test Suite

website/contents/contributing/testing.md

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+---
+path: "contributing/testing"
+title: "Testing"
+hasPlayground: false
+---
+
+# Testing
+
+Yoga tries to be as close as possible to chrome in its flexbox behaviour.
+To ensure this most of Yoga's test suite is automatically generateded from
+running the corresponding layout in chrome using a webdriver which then generates 
+C++ test which asserts that Yoga will produce matching outputs for that layout.
+
+## Running the Test Suite
+
+1. Yoga builds with [buck](https://buckbuild.com). Follow their documentation to get up and running.
+2. For testing Yoga relies on [gtest](https://github.com/google/googletest) as a submodule. After cloning Yoga run `git submodule init` followed by `git submodule update`.
+3. In a terminal from the root of your Yoga checkout run `buck test //:yoga`.
+
+## Adding a Test
+
+Instead of manually writing a test which ensures parity with web implementations
+of Flexbox we make use of a generated test suite. We use `gentest/gentest.rb` to
+generate this test suite. Write the html which you want to verify in Yoga and put
+it in the `gentest/fixtures` folder, such as the following.
+
+```html
+<div id="my_test" style="width: 100px; height: 100px; align-items: center;">
+  <div style="width: 50px; height: 50px;"></div>
+</div>
+```
+
+Run `gentest/gentest.rb` to generate test code and re-run `buck test //:yoga`
+to validate the behavior. One test case will be generated for every root `div`
+in the input html with the string in the `id` corresponding to the test name.
+
+You may need to install the latest watir gem (`gem install watir`) and
+[ChromeDriver](https://sites.google.com/a/chromium.org/chromedriver/) to
+run `gentest/gentest.rb` Ruby script.
+
+## Manual test
+
+For some aspects of Yoga we cannot generate a test using the test generation
+infrastructure described earlier. For these cases we manually write a test in 
+the `/tests` directory.