import FIREFOX_52_6_0esr_RELEASE from mozilla-esr52 hg repo

testing/web-platform/tests/docs/running_tests.md

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+In simple cases individual tests can be run by simply loading the page
+in a browser window. For running larger groups of tests, or running
+tests frequently, this is not a practical approach, and several better
+options exist.
+
+## From Inside a Browser
+
+For running multiple tests inside a browser, there is the test runner,
+located at
+
+    /tools/runner/index.html
+
+This allows all the tests, or those matching a specific prefix
+(e.g. all tests under `/dom/`) to be run. For testharness.js tests,
+the results will be automatically collected, whilst the runner
+provides a simple UI for manually comparing reftest rendering and
+running manual tests.
+
+Because it runs entirely in-browser, this runner cannot deal with
+edge-cases like tests that cause the browser to crash or hang.
+
+## By Automating the Browser
+
+For automated test running designed to be robust enough to use in a CI
+environment, the [wptrunner](http://github.com/w3c/wptrunner) test runner
+can be used. This is a test runner written in Python and designed to
+control the browser from the outside using some remote control
+protocol such as WebDriver. This allows it to handle cases such as the
+browser crashing that cannot be handled by an in-browser harness. It
+also has the ability to automatically run both testharness-based tests
+and reftests.
+
+Full instructions for using wptrunner are provided in its own
+[documentation](http://wptrunner.readthedocs.org).