High Coverage but Tests Miss Defects

Test coverage numbers look healthy but defects still reach production.
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  3 minute read  

What you are seeing

Your dashboard shows 80% or 90% code coverage, but bugs keep getting through. Defects show up in production that feel like they should have been caught. The team points to the coverage number as proof that testing is solid, yet the results tell a different story.

People start losing trust in the test suite. Some developers stop running tests locally because they do not believe the tests will catch anything useful. Others add more tests, pushing coverage higher, without the defect rate improving.

Common causes

Inverted Test Pyramid

When most of your tests are end-to-end or integration tests, they exercise many code paths in a single run - which inflates coverage numbers. But these tests often verify that a workflow completes without errors, not that each piece of logic produces the correct result. A test that clicks through a form and checks for a success message covers dozens of functions without validating any of them in detail.

Read more: Inverted Test Pyramid

Pressure to Skip Testing

When teams face pressure to hit a coverage target, testing becomes theater. Developers write tests with trivial assertions - checking that a function returns without throwing, or that a value is not null - just to get the number up. The coverage metric looks healthy, but the tests do not actually verify behavior. They exist to satisfy a gate, not to catch defects.

Read more: Pressure to Skip Testing

Code Coverage Mandates

When the organization gates the pipeline on a coverage target, teams optimize for the number rather than for defect detection. Developers write assertion-free tests, cover trivial code, or add single integration tests that execute hundreds of lines without validating any of them. The coverage metric rises while the tests remain unable to catch meaningful defects.

Read more: Code Coverage Mandates

Manual Testing Only

When test automation is absent or minimal, teams sometimes generate superficial tests or rely on coverage from integration-level runs that touch many lines without asserting meaningful outcomes. The coverage tool counts every line that executes, regardless of whether any test validates the result.

Read more: Manual Testing Only

How to narrow it down

  1. Do most tests assert on behavior and expected outcomes, or do they just verify that code runs without errors? If tests mostly check for no-exceptions or non-null returns, the problem is testing theater - tests written to hit a number, not to catch defects. Start with Pressure to Skip Testing.
  2. Are the majority of your tests end-to-end or integration tests? If most of the suite runs through a browser, API, or multi-service flow rather than testing units of logic directly, start with Inverted Test Pyramid.
  3. Does the pipeline gate on a specific coverage percentage? If the team writes tests primarily to keep coverage above a mandated threshold, start with Code Coverage Mandates.
  4. Were tests added retroactively to meet a coverage target? If the bulk of tests were written after the code to satisfy a coverage gate rather than to verify design decisions, start with Pressure to Skip Testing.

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