Refactoring Breaks Tests

Internal code changes that do not alter behavior cause widespread test failures.
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  2 minute read  

What you are seeing

A developer renames a method, extracts a class, or reorganizes modules - changes that should not affect external behavior. But dozens of tests fail. The failures are not catching real bugs. They are breaking because the tests depend on implementation details that changed.

Developers start avoiding refactoring because the cost of updating tests is too high. Code quality degrades over time because cleanup work is too expensive. When someone does refactor, they spend more time fixing tests than improving the code.

Common causes

Inverted Test Pyramid

When the test suite is dominated by end-to-end and integration tests, those tests tend to be tightly coupled to implementation details - CSS selectors, API response shapes, DOM structure, or specific sequences of internal calls. A refactoring that changes none of the observable behavior still breaks these tests because they assert on how the system works rather than what it does.

Unit tests focused on behavior (“given this input, expect this output”) survive refactoring. Tests coupled to implementation (“this method was called with these arguments”) do not.

Read more: Inverted Test Pyramid

Tightly Coupled Monolith

When components lack clear interfaces, tests reach into the internals of other modules. A refactoring in module A breaks tests for module B - not because B’s behavior changed, but because B’s tests were calling A’s internal methods directly. Without well-defined boundaries, every internal change ripples across the test suite.

Read more: Tightly Coupled Monolith

How to narrow it down

  1. Do the broken tests assert on internal method calls, mock interactions, or DOM structure? If yes, the tests are coupled to implementation rather than behavior. This is a test design issue - start with Inverted Test Pyramid for guidance on building a behavior-focused test suite.
  2. Are the broken tests end-to-end or UI tests that fail because of layout or selector changes? If yes, you have too many tests at the wrong level of the pyramid. Start with Inverted Test Pyramid.
  3. Do the broken tests span multiple modules - testing code in one area but breaking because of changes in another? If yes, the problem is missing boundaries between components. Start with Tightly Coupled Monolith.

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