Typical causes include:

• Improper initialization or cleanup.
• Invalid assumptions about the state of test data.
• Invalid assumptions about the state of the system. An example can be the system time.
• Dependencies on the timing of the application.
• Dependencies on the order in which the tests are run. (Similar to the first case above.)

An unreliable test-running framework can introduce flakiness. Typical causes include:

• Failure to allocate enough resources for the system under test thus causing it to fail coming up.
• Improper scheduling of the tests so they “collide” and cause each other to fail.
• Insufficient system resources to satisfy the test requirements.

• Being slow to respond or being unresponsive to the stimuli from the tests.
• Networking failures or instability.
• Resources being consumed by other tasks/services not related to the tests being run.

• Timeouts are not long enough. Solution: get sign from UI that action finished.