A flaky test changes outcome without an intended code change. Common causes include races, shared state and uncontrolled external dependencies.
Before you start
You should understand inputs, expected outputs and the boundaries of the component under test. State the risk a test should detect before choosing a tool or mock. Distinguish controlled dependencies from real integrations so the result does not imply more coverage than the test actually provides.
The practical goal is to reason through this situation: A test passes alone but fails in a suite because another test changes global configuration. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Capture variability
Record order, environment and timing when outcomes change.
Step 2: Control one suspected cause
Isolate shared state or completion order before adding retries.
Step 3: Fix ownership
Eliminate the race or leak rather than merely masking its visible failure.
Worked scenario
A test passes alone but fails in a suite because another test changes global configuration.
A test passes alone but fails after another test changes timezone configuration. Retrying may happen to run it under a restored state, hiding the dependency. Give each test owned configuration setup and cleanup or inject the relevant setting explicitly, then confirm both execution orders produce the same outcome.
Common mistake
Automatic retries can reduce noise while hiding the underlying fault.
Verify the behavior
Run varied orders and repeated executions with the suspected shared state controlled.
Interview exercise
Investigate one flake.
Answer and reasoning
Capture order, timing and environment, reproduce under controlled variation and fix the shared ownership or synchronization issue.
Continue learning
Compare the scenario with the Software Testing interview questions and test your understanding with the Software Testing MCQs. For terminology and implementation details, consult the reference material.