Add Chromium for iOS test documentation.

Create documentation on how to run different iOS test suites.

TBR: huangml
Bug: 769753
Change-Id: I1e63c6c603a10389ccc89050b01e075fd08e39ae
Reviewed-on: https://chromium-review.googlesource.com/772784Reviewed-by: Mike Baxley <baxley@chromium.org>
Commit-Queue: Mike Baxley <baxley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517095}

docs/README.md

@@ -252,6 +252,7 @@ used when committed.
     iOS app open links in Chrome.
 *   [User Agent in Chrome for iOS](ios/user_agent.md) - Notes on User Agent
     strings using Chrome for iOS.
+*   [Running iOS test suites locally](ios/testing.md)
 
 ### Media
 *   [Audio Focus Handling](media/audio_focus.md) - How multiple MediaSession

docs/ios/testing.md

+# Automated testing for Chrome for iOS
+
+See the [instructions] for how to check out and build Chromium for iOS.
+
+Automated testing is a crucial part of ensuring the quality of Chromium.
+
+## Unit testing
+
+Unit testing is done via gtests. To run a unit test, simply run the test
+target (ending in _unittest).
+
+## Integration testing
+
+[EarlGrey] is the integration testing framework used by Chromium for iOS.
+
+### Running EarlGrey tests
+
+EarlGrey tests are based on Apple's [XCUITest].
+
+#### Running tests from Xcode
+
+An entire suite of tests can be run from Xcode.
+1. Select the *egtest target you wish to run.
+2. ⌘+U to run all the tests. Note: ⌘+R, which is normally used to run an
+application, will simply launch the app under test, but will not run the
+XCTests.
+
+A subset of tests can be run by selecting the test or test case from the
+XCTest navigator on the left side of the screen.
+
+#### Running from the command-line
+
+When running from the command-line, it is required to pass in the *.xctest
+target, in addition to the test application.
+Example:
+```
+./out/Debug-iphonesimulator/iossim -d "iPad Retina" -s 8.1 \
+out/Debug-iphonesimulator/ios_chrome_integration_egtests.app \
+out/Debug-iphonesimulator/ios_chrome_integration_egtests_module.xctest
+```
+
+
+[EarlGrey]: https://github.com/google/EarlGrey
+[instructions]: ./build_instructions.md
+[XCUITest]: https://developer.apple.com/documentation/xctest