[Creating] How to use JUnit

What is JUnit

"JUnit" is a framework for Java unit testing. You can verify that it works correctly by writing a unit test.

Test rules in JUnit

--If the class name to be tested is "Xxx", the test class name will be "XxxTest". --If the method name to be tested is "Yyy", the test method name will be "testYyy". --Add annotation "@Test" to the test method. Make it "public void" --The test method is "assertThat (actual value, is (expected value));" --Write code that makes "prerequisites, execution, verification" easy to understand

Basic usage

The basic usage is as follows.

Sample.java


public class Sample {
  public static int toDouble(int num) {
    return num * 2;
  }
}

Here's a JUnit test for the sample above:

SampleTest.java


import org.junit.Test;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.*;

public class SampleTest {
  @Test
  public void testToDouble() {
    int actual = Sample.toDouble(10);
    int expect = 20;
    assertThat(actual, is(expect));
  }
}

If it does not return the expected value, the test will fail as follows:

java.lang.AssertionError:
Expected: is <21>
     but: was <20>

Temporarily ignore the test: @ignore

You can temporarily ignore the test by giving @Ignore.

@Ignore @Test
public void doSomething() { /* ... */ }

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