Should you write unit tests for legacy code?

If you are planning on refactoring the legacy code then creating those unit tests is a must. Don’t worry about mocking or stubbing – worry about testing the inputs and outputs of the system so that your changes or refactoring efforts don’t break current functionality.

What is legacy code in testing?

Legacy code is source code inherited from someone else or inherited from an older version of the software. It can also be any code that you don’t understand and that’s difficult to change.

Can you unit test a protected method?

Protected is a kind of different discussion point, but in summary, it should not be there at all. Either it breaks encapsulation on deployed code, or it forces you to inherit from that class, just to unit test it, even sometimes you do not need to inherit.

What methods should be unit tested?

9 Essential Unit Test Best Practices

Tests Should Be Fast.
Tests Should Be Simple.
Test Shouldn’t Duplicate Implementation Logic.
Tests Should Be Readable.
Tests Should Be Deterministic.
Make Sure They’re Part of the Build Process.
Distinguish Between The Many Types of Test Doubles and Use Them Appropriately.

How do you write a unit test for legacy code?

Here’s some tips to adding tests to legacy code.

Start Somewhere. When creating a new feature or fixing a bug, take some time to think about how to write some tests about the changes you’re implementing.
Incrementally. Add tests as part of your daily workflow.
Take on Technical Debt.

How do you write a legacy code test?

Should you unit test private methods?

Unit Tests Should Only Test Public Methods The short answer is that you shouldn’t test private methods directly, but only their effects on the public methods that call them. Unit tests are clients of the object under test, much like the other classes in the code that are dependent on the object.

Do I need to test protected methods?

Generally, it is recommended to test only those protected methods directly that are part of the class’ API, i.e., that are explicitly intended to be used by subclasses. All other protected methods should be tested indirectly through the existing public methods.

How do you write an effective unit test?

13 Tips for Writing Useful Unit Tests.
Test One Thing at a Time in Isolation.
Follow the AAA Rule: Arrange, Act, Assert.
Write Simple “Fastball-Down-the-Middle” Tests First.
Test Across Boundaries.
If You Can, Test the Entire Spectrum.
If Possible, Cover Every Code Path.
Write Tests That Reveal a Bug, Then Fix It.

Is it worth it to add unit tests to legacy code?

The book The Art of Unit Testing has some good advice on this. It also recommends the book Working Effectively with Legacy Code; I haven’t read the latter yet, but it’s on my stack. EDIT: But yes, even minimal code coverage was worthwhile. It gave me confidence and a safety net for refactoring the code.

When do assertions fail in a unit test?

In such tests, written after the facts, assertions verify the current behavior of the code. Unlike unit tests, they do not prove that the code is correct, they are just pinning down (characterizing) the current behavior of the code. The tests will fail if you modify the external behavior of the code.

Why is code coverage important for unit tests?

Not at all, but it has a clear relationship to how well-tested the code is, which in turn is our best way to increase confidence in its correctness. Code coverage is a measurable approximation of immeasurable qualities we care about. Some specific cases where having an empirical standard could add value:

How are unit tests used in characterization tests?

A unit test framework such those of the xUnit family can be used to write characterization tests. In such tests, written after the facts, assertions verify the current behavior of the code. Unlike unit tests, they do not prove that the code is correct, they are just pinning down (characterizing) the current behavior of the code.

Should you write unit tests for legacy code?