An introduction to code coverage explaining what it measures, how to generate it with Jest, and how to interpret the four key metrics: statement, branch, function, and line coverage. Uses a FizzBuzz example to demonstrate how 100% coverage can still miss bugs — specifically showing how tests can execute all code paths without verifying correctness. Recommends using coverage as a workflow tool for code review and edge-case discovery rather than chasing a specific percentage target.
Table of contents
Code coverageHow toAn exampleOur first testInterpreting our code coverageCode coverage in your workflowConclusion9 Impressions