Note: The detailed writing method is not written. I've just put together a Techscore JUnit page. Please refer to here for how to write a unit test.

What is a unit test?

A test to make sure that the code you write works as expected. Also called a unit test. JUnit is a very famous framework for unit testing in Java. Writing test programs using a common framework makes it easier for others to modify their test programs.

Super basic flow of testing

1. Write a test method that has the same functionality as the method you want to test.
Compare the result required for the method with the actual result using the assert method (below).
1. If there is a difference in the comparison results, the test fails, otherwise the test succeeds.

Setup (using IntelliJ)

https://stackoverflow.com/questions/19330832/setting-up-junit-with-intellij-idea https://www.slideshare.net/SatoshiKubo1/junitjava

type of assert method

Various asserts are used to confirm the test results. assertEquals() → Determine if the expected result is the same as the actual result. Argument 1: (expected, actual) Argument 2: (String message, expected, actual) --A message is displayed if the test fails. Argument 3: (expected, actual, delta) --delta is the tolerance. Argument 4: (String message, double expected, double actual, double delta)- assertNotNull() → Judge whether the given Object is not null. Argument 1: (Object object) Argument 2: (String message, Object object) --A message is displayed if the test fails. assertNull() → Judge whether the given Object is Null. Argument 1: (Object object) Argument 2: (String message, Object object) --A message is displayed if the test fails. assertSame() → Judge whether the given two Objects refer to the same Object. Argument 1: (Object expected, Object actual) Argument 2: (String message, Object object) --A message is displayed if the test fails. assertTrue() → Judge whether the given conditions are correct. Argument 1: (Object expected, Object actual) Argument 2: (String message, Object object) --A message is displayed if the test fails. assertThat() In combination with Matcher, it is more convenient than assertEquals (). There is a limit to assertEquals () because only one equals () can be created for an object. Since it is Matcher, not assertThat, that is verified, it is highly extensible. The situation of writing assert Equals on multiple lines no longer occurs. Arguments: (Object actual, Matcher matcher) Details

important point

The order doesn't matter

The methods in the test class are not executed in order from the top. Therefore, do not write test methods that assume the above test results.

Does not create side effects

Do not create "side effects" that change the state of the system, such as updating the database when testing.

Give a descriptive method name

So that those who read the code later can quickly understand the purpose of the test.

Write easy-to-understand code

Same as above. Simple and easy to understand without waste.

Document your test plan in javadoc

Writing manually + many mistakes + hard to keep up with updates.

As small and fast as possible

To be able to test frequently and easily.

Other useful methods

If you want to perform common processing (database connection / disconnection, etc.) at the beginning and end of multiple methods, use the setUp () and tearDown () methods. setUp() Executed before each test method is called. tearDown() Executed after the end of each test method.

TestSuite class

As mentioned above, the test methods are not executed in the order they are written, but you can use the TestSuite class to specify the order in which the test methods are executed.

Reference source

JUnit | Techscore -assertEquals is old | I like Java -Unit Test Improvement Guide | Developers.IO -I want to remember this, 4 designs for writing unit tests | Qiita -Note on how to use the methods defined in Hamcrest's Matchers | Qiita

[JAVA] Introduction to JUnit (study memo)