Is there any option to run it in multiple engines.

I want to run the tests in multiple engines slimerjs and phantomjs. Is there any option to specify that in backstop.json like eg : `"engine" : ["slimerjs","phantomjs"],`

Start by reviewing how backstop.json currently represents the test engine. Determine the expected behavior for specifying both slimerjs and phantomjs, including whether tests should run in each engine. Done means the configuration can express both engines and the test suite executes successfully against both.

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