Test coverage
Coverage can measure a few genuinely different things. Code coverage is the percentage of lines, branches, or functions in the codebase that get executed by the test suite. Requirements coverage is the percentage of documented requirements with at least one test verifying them. Feature coverage is a less formal sense of how thoroughly a given feature's behavior is actually tested. These measure different things, and a tool reporting a coverage percentage without saying which kind is reporting a number without much meaning on its own.
A hundred percent code coverage isn't the goal it sounds like. A line of code can execute during a test without that test actually asserting anything meaningful about what happened, which is how a suite can report high code coverage while still missing a real defect, closely related to the problem of a false negative. Coverage measures whether code ran, not whether it was checked correctly, which is why a thoughtful team treats coverage as one signal among several, not a target to maximize for its own sake.
Used well, coverage is genuinely valuable for finding what's completely untested, a function or a branch nobody's test suite ever touches is a real, concrete gap, not a theoretical one. It's also useful as a trend, watching coverage drop on a specific area after a change is a signal worth investigating, even if the absolute number isn't meaningful on its own. Used that way, as a tool for finding gaps and tracking trends rather than a score to chase, it earns its place.
Types of coverage
- Code coverage, the percentage of lines, branches, or functions actually executed by the test suite.
- Requirements coverage, the percentage of documented requirements with at least one test verifying them.
- Feature coverage, a less formal sense of how thoroughly a given feature's behavior is actually exercised.
- Each measures something different, a single number labeled coverage without specifying which kind doesn't say much on its own.
Where it shows up
- A code coverage report flagging a function that no test in the suite ever actually executes.
- A requirements traceability report showing which documented requirements still have zero test cases verifying them.
- Coverage dropping on a specific module after a change, prompting a team to investigate whether new tests are actually needed there.
- A team treating a coverage target, like 80%, as a floor worth investigating gaps below, not a score to chase for its own sake.
Benefits and challenges
| Benefit | Challenge |
|---|---|
| Finds code or a requirement with zero test coverage, a real, concrete gap rather than a theoretical one. | High coverage doesn't guarantee good testing, code can execute during a test without the test actually checking anything meaningful about it. |
| Useful as a trend, a sudden drop in coverage on a specific area is a signal worth investigating. | Chasing a coverage percentage as a target encourages writing shallow tests just to execute a line, rather than genuinely useful ones. |
| Gives a concrete, measurable signal where testing effort might otherwise be a guess. | Different kinds of coverage, code, requirements, feature, measure different things, and conflating them leads to a misleading picture. |
Frequently asked questions
Should a team aim for 100% code coverage?
Usually not as a goal in itself. Some code, like simple getters or generated boilerplate, isn't worth the effort to specifically test, and chasing the last few percent often means writing shallow tests that execute a line without meaningfully checking it. Most teams set a reasonable floor and investigate gaps below it, rather than maximizing the number.
Does high test coverage mean the application is well tested?
Not necessarily. Coverage measures whether code ran during a test, not whether the test actually verified the right thing happened. A suite can report high coverage and still miss a real defect if its assertions are too shallow, which is why coverage is one signal among several, not the whole picture.
What's the difference between code coverage and requirements coverage?
Code coverage measures how much of the actual source code gets executed by tests. Requirements coverage measures how many documented requirements have at least one test verifying them. A codebase can have high code coverage while a real requirement still has no test checking it, since the two measure different things entirely.
How Klarent helps
Klarent's AI agents generate tests tied to a described user flow, which naturally maps toward requirements and feature coverage, helping a team see which real scenarios are actually tested rather than relying on a code coverage percentage alone.