Question: isparta doesnt seem to work well with files .es6 extension

I'm trying to get the code coverage working in my project that I recently enabled babel6. I have the es6 files with .es6 extension and es5 files with .js extension.
The babel-node node_modules/.bin/isparta cover _mocha doesn't work well. I use grunt for my build and grunt-mocha-test for running my test cases (test cases are *.es6 and *.js). I don't have luck with code coverage so far with isparta. Any pointers here are appreciated.

The report names the command `babel-node node_modules/.bin/isparta cover _mocha` and test files using `.es6` and `.js` extensions, but no repository file or failing test. Start by reproducing the command with the project's test setup; done would require a working coverage path for both extensions, though the issue gives no concrete expected output or fixture.

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