coverage-mode is an Emacs minor mode that enables the highlighting of lines within buffers to indicate their code coverage status, as determined by your test suite.

coverage-mode is available on MELPA and MELPA-STABLE

You can install coverage-mode with the following command.

M-x package-install [RET] coverage [RET]

To enable coverage-mode in the current buffer, use M-x coverage-mode RET.

Repeat this command to disable coverage-mode for the current buffer.

Once enabled in a buffer, highlighting will be automatically updated as the test coverage for that file changes. You may enable and disable coverage-mode independently for multiple files in the same project.

Currently coverage-mode only works with output as supplied by the SimpleCov gem.

By default, coverage-mode looks in your current vc-git-root directory for the coverage/.resultset.json file. You can configure this to whatever filepath you want through the Coverage Dir customization variable.

You can also choose your own faces for covered & uncovered lines through customization variables. These default to green for covered & red for uncovered.

You may also wish to customize coverage-interval if you want more (or less) responsive coverage highlight updates.