JUnit basis for Android unit testing (1)

When creating a project with Android Studio, three folders main, test, and androidTest will be generated in the src folder at the same time.

test and androidTest are specifically for source-level white-box testing.
test: The folder is used to write unit tests that do not depend on the device environment, which can be run directly on the PC;
androidTest: The folder is used to write tests that need to be run on the device.

Classification

Functional testing: has nothing to do with UI, test IO operations, algorithms, processes, etc.
UI testing: test UI interaction logic, such as clicks, logins, etc.

Java unit testing framework: JUnit , Mockito , etc.;
Android: AndroidJUnitRunner , Espresso , etc.

This article mainly introduces the common annotations and assertions of JUnit and their basic use. Other testing frameworks will be introduced in subsequent blog posts.
JUnit

rely:

dependencies {
    testCompile 'junit:junit:4.12'
}

Common annotations and assertions:

Each test method in Junit3 must start with test, and annotations are added in Junit4, and there is no requirement for method names.
Example:
Create a calculation tool class

/**
 * Created by scy on 2018/4/26.
 */

public class Calculater {
    public int sum(int a, int b){
        return a+b;
    }

    public int substract(int a, int b){
        return a-b;
    }

    public int divide(int a, int b){
        return a/b;
    }

    public int multiply(int a, int b){
        return a*b;
    }
}

Then follow the steps below

Note: 1 Select the method to be tested 2 Click OK 3 Select the test class generation location

Automatically create test classes:

Pay attention to the import package import static org.junit.Assert.*;and then modify the code:

/**
 * Created by scy on 2018/4/26.
 */
public class CalculaterTest {

    private Calculater mCalculator;
    private int a = 1;
    private int b = 3;

    @Before//在测试开始之前回调的方法
    public void setUp() throws Exception {
        mCalculator = new Calculater();
    }


    @Test//我们需要测试的方法
    public void sum() throws Exception {
        int result = mCalculator.sum(a, b);
        // 第一个参数："sum(a, b)" 打印的tag信息 （可省略）
        // 第二个参数： 3 期望得到的结果
        // 第三个参数  result：实际返回的结果
        // 第四个参数  0 误差范围（可省略）
        assertEquals("sum(a, b)",3,result,0);
    }

    @Test
    public void substract() throws Exception {
        int result = mCalculator.substract(a, b);
        assertEquals(-3,result，2);
    }

}

If the expected value and the actual value are within the error range, the test passes, otherwise the test fails!
Android Studio right-clicks the class -> run CalculaterTest, and all methods annotated with @Test in the use case will be executed. The above test results are as follows:

it shows that there is an error sum()method that expects to get 3 and actually returns 4, the error is 0, so it fails; while the second method substract()expects to get -3 and actually returns -2 but within the error range of 2, so the test passes.
If the code is changed sum() ->Assert.assertEquals(4,result);, the tests will all pass.
Here is a sample assertion from w3c:

/**
 * Created by scy on 2018/4/27.
 */
public class AssertTest {
    @Test
    public void testAssertions() {
        //test data
        String str1 = new String("abc");
        String str2 = new String("abc");
        String str3 = null;
        String str4 = "abc";
        String str5 = "abc";
        int val1 = 5;
        int val2 = 6;
        String[] expectedArray = {"one", "two", "three"};
        String[] resultArray = {"one", "two", "three"};

        //Check that two objects are equal
        assertEquals(str1, str2);

        //Check that a condition is true
        assertTrue(val1 < val2);

        //Check that a condition is false
        assertFalse(val1 > val2);

        //Check that an object isn't null
        assertNotNull(str1);

        //Check that an object is null
        assertNull(str3);

        //Check if two object references point to the same object
        assertSame(str4, str5);

        //Check if two object references not point to the same object
        assertNotSame(str1, str3);

        //Check whether two arrays are equal to each other.
        assertArrayEquals(expectedArray, resultArray);
    }
}

Reference
Testing Getting Started Guide
Official Testing Tutorial
Unit Testing in Android
w3c