Deterministic tests in JUnit - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for a test to be deterministic?

A deterministic test always produces the same result when run with the same input and environment, ensuring reliability and predictability.

beginner

Why are deterministic tests important in software testing?

They help identify real bugs by avoiding false failures caused by randomness or external factors, making debugging easier and builds more stable.

intermediate

How can you make a test deterministic when it involves random data?

Use a fixed seed for random number generators so the sequence of random values is the same every time the test runs.

intermediate

In JUnit, what practice helps ensure tests are deterministic when dealing with time-dependent code?

Mock or control the system clock or time source so the test always uses a fixed, known time.

beginner

What is a common cause of non-deterministic tests?

Tests that depend on external systems, network, or shared state without isolation can behave differently each run.

What characteristic defines a deterministic test?

A Depends on external services

B Runs faster than other tests

C Uses random data every time

D Always produces the same result given the same input

Deterministic tests always produce the same result when run with the same input and environment.

How can you control randomness in a JUnit test to make it deterministic?

A Avoid assertions

B Run the test multiple times

C Use a fixed seed for the random number generator

D Use external APIs

Using a fixed seed ensures the random values are the same every test run.

Which of the following can cause a test to be non-deterministic?

A Relying on current system time without control

B Using a fixed system clock

C Mocking external dependencies

D Setting fixed input data

Using the current system time without control can cause different results each run.

Why should tests avoid depending on external systems?

A To reduce test execution time

B To ensure tests are deterministic and reliable

C To increase code complexity

D To use more network bandwidth

Avoiding external dependencies helps keep tests deterministic and reliable.

What is a good practice to make time-dependent tests deterministic in JUnit?

A Mock the system clock to return a fixed time

B Use Thread.sleep() to wait

C Run tests only at night

D Ignore time in assertions

Mocking the system clock ensures consistent time values during tests.

Explain what deterministic tests are and why they matter in software testing.

Think about tests giving the same result every time.

Describe strategies to make tests deterministic when they involve randomness or time.

Consider how to control variables that change each run.