Jest is a delightful tool for JavaScript testing from Facebook. As your project evolves and you add tests (or perhaps choose to not add tests) you may wonder what kind of test coverage you have. What is the overall coverage? Which files are well covered and which are seriously lacking?
Use the --coverage flag to get this information.
$ jest --coverageAfter running all of your tests a table will be output to the terminal with a list of files and their respective coverage percentages in terms of statement, branch, function, and line coverage.
---------------------------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
---------------------------|----------|----------|----------|----------|----------------|
This can help guide you to what parts of your app may need more testing.