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Automated tests can pass while a real bug remains because a green result means only that the checks that ran met their programmed expectations. It does not show that the broken behavior was tested, that the expected result was correct, or that the checks observed the kind of outcome that failed.
What a green test run does—and does not—tell you
A passing run is evidence about a particular set of tests, inputs, assertions, and execution conditions. It tells you those checks did not report a failure. It does not prove that every important path works or that the tests’ assumptions match the product’s requirements. ISTQB’s testing-principles material describes this basic limit: testing cannot prove the absence of defects (ISTQB Guru, “The 7 Principles of Software Testing (ISTQB) with Real Examples”).
When a defect escapes, trace the chain: what the user or requirement expects, what behavior the test exercises, which part of the system it reaches, and what its assertion actually checks. Four gaps in that chain explain many apparently contradictory outcomes.
1. The broken path has no check
A suite can be green because it never runs the journey or edge case where the defect occurs. Imagine a checkout flow with tests for adding an item and viewing a cart, but no test for applying a discount at payment. Those passing tests say nothing about the untested discount path.
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How to investigate
- Start from the reported symptom and reproduce the exact user journey, including relevant inputs and state.
- Find the tests that claim to cover that requirement. Confirm that they execute the affected branch and assert the user-visible result, not merely that no exception occurred.
- Add a focused regression test for the missed case, then run it against the fixed code and the surrounding suite.
AxonBuild describes audited examples in which the relevant path lacked a working test; that illustrates a coverage gap, not proof that adding a test by itself guarantees correctness (Bilal Shahid, AxonBuild, August 28, 2026).
2. The test expects the wrong result
A test can faithfully confirm an incorrect expectation. If a requirement is misunderstood—or if a test is generated from faulty assumptions—the assertion may bless the bug. For example, AxonBuild’s article illustrates a generated test that expected division by zero to return zero. That is the article’s example, not a universal pattern; the broader issue is that the test’s expected result itself can be wrong.
Check the oracle, not just the implementation
The test oracle is the basis for deciding whether an observed result is correct. Before trusting a passing assertion, compare its expected value with an independent source of truth: an approved requirement, a domain rule, a documented interface contract, or a manually reasoned example. Avoid deriving the expected result from the same implementation being tested; doing so can reproduce its mistake.
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- Ask who decided the expected outcome and what requirement supports it.
- Use boundary and contrasting examples where possible, so an assertion cannot pass for a broad range of incorrect behavior.
- When the requirement is ambiguous, resolve it with the responsible product or domain owner before treating the test as authoritative.
3. A test double hides the production behavior
A mock or stub can make a test faster and more predictable, but it also replaces real behavior. If the defect is in the code replaced by the test double—or in how production components interact—the test may exercise only the substitute and never reach the faulty path.
AxonBuild reports a checkout example where the suite did not call the code that created a sale. That is a specific account from its article, rather than an independently verified finding about checkout systems generally (AxonBuild).
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Choose the boundary deliberately
Mocks are useful for isolating a unit or simulating an external dependency. They are not evidence that the real dependency, integration, or production wiring works. Keep unit tests focused, then add integration or end-to-end checks at boundaries where real components must cooperate. For a suspected escape, inspect what the test double replaces and verify that at least one suitable test exercises the actual production code relevant to the behavior.
4. The tests check function, not appearance
A workflow can remain usable to an automated functional test while its interface is visibly broken. A test might confirm that registration succeeds, yet miss a dialog whose buttons overlap, appear off-screen, or are misplaced. Qt describes this kind of green-test/UI-defect mismatch: the checks established functional behavior, not visual correctness (Qt, “Automated Tests Are ‘Green’ But Your UI Is Broken”).
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Match the check to the requirement. If the requirement concerns layout, visual hierarchy, or responsive rendering, a test that only clicks controls is insufficient. Use an appropriate visual assertion or review the rendered screen at relevant viewport sizes. Visual checks can themselves be sensitive to fonts, rendering environments, and dynamic content, so define which differences matter rather than treating every pixel change as a product defect.
Capturing screenshots for visual review
A browser-based screenshot can provide an artifact for manual review or for a visual-comparison system, but a captured image alone does not determine whether the UI is correct. The expected appearance and comparison criteria still need to be defined. For a manual capture, use browser developer tools or an existing test framework to render the page at the viewport and state that failed, then inspect the result against the design requirement.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to respond when tests pass but the app is broken
- Reproduce the failure. Record the route, input, account or application state, viewport, and sequence needed to see it.
- Locate the nearest relevant test. Determine whether it covers the exact path, uses real production behavior where needed, and asserts the failed outcome.
- Validate the expectation. Check that the assertion reflects the requirement rather than the current implementation or an assumption copied from it.
- Use a check suited to the defect. Functional assertions do not automatically verify appearance, usability, performance, or other properties outside their scope.
- Add a focused regression check. Make the test fail on the defect and pass after the fix; retain exploratory or visual review for requirements that are not adequately represented by automated assertions.
Neither a pass rate nor a coverage percentage answers all four questions: Was the affected requirement covered? Did the check reach the relevant real code? Was its expected result correct? Did it observe the kind of outcome that failed? Mozilla’s guidance on analyzing automated-test results likewise treats results as something to interpret rather than an infallible statement about software quality (Mozilla Test Engineering, March 4, 2014).
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If a failed requirement is visual, you can capture a page for review with ScreenshotNeo, a website screenshot API and MCP server. A capture is evidence to inspect, not a verdict that the UI is correct.
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