Introduction to Android UT development

I. Overview

        Android UT (Unit Testing) development refers to the development process of unit testing in Android applications. Unit testing is a software testing method used to test the correctness of the smallest testable unit (usually a function or method) in an application.

The main goal of Android UT development is to ensure that the various units of the application function correctly and as expected under different circumstances. By writing, running, and maintaining unit tests, developers can identify and resolve potential problems early, improving code quality and reliability.

The following are the general steps for Android UT development:

• Determine the goal of unit testing: Select the specific unit (function, method, etc.) to be tested and understand its expected behavior and input and output.
• Create test cases: Write test cases that include test data and expected results for different inputs and situations.
• Integrate testing frameworks: Choose suitable testing frameworks (such as JUnit, Mockito, etc.) and integrate them in Android applications.
• Write test code: Use the selected test framework to write test code that calls the unit under test and asserts that the expected results are consistent with the actual results.
• Run tests: Run the test code in the development environment and ensure that the test results are as expected.
• Analyze results: Analyze the coverage and execution results of the test code to find possible problems and potential errors.
• Fix the problem: If a test finds an issue or bug, the developer should fix the associated code and rerun the test to ensure the issue is resolved.
• Continuous integration: Integrate unit testing with the continuous integration process to ensure that relevant unit tests are run for every code change.

        Through systematic unit test development, you can improve the robustness, maintainability, and testability of your code and reduce the risk of introducing new bugs. At the same time, it can also help developers better understand and master the behavior and logic of the code.

2. Simple example

1. Introduction to JUnit

        JUnit is an open source framework for writing and running unit tests. It is one of the most popular unit testing frameworks in Java development and is used to test various components, methods, and functions of Java applications.

The main features and advantages of JUnit are as follows:

Easy to use : JUnit provides a concise and intuitive set of APIs that are easy to learn and use. It uses annotations and assertions to write test code, making writing and running unit tests simple and straightforward.

Automated testing : JUnit supports automated testing, which means you can write a test once and then run it repeatedly to ensure that the code remains correct throughout the development process. This saves a lot of time and effort in manual testing.

Test-driven development : JUnit encourages the practice of test-driven development (TDD). By writing tests first and then writing code that passes those tests, JUnit can help developers better define the expected behavior and functionality of their code and ensure that the code runs correctly according to those requirements.

Assertion and verification : JUnit provides a wealth of assertion and verification methods to verify whether the output results and behavior of the code are as expected. This ensures the logic of your code is correct and catches potential errors.

Test suites and extensibility : JUnit supports the creation of test suites, which can combine multiple test classes to run together. At the same time, JUnit also supports extensions, and custom extension points can be used to enhance the functionality of the testing framework.

Continuous integration : JUnit seamlessly integrates with continuous integration tools (such as Jenkins) to easily integrate unit testing with the build process and code deployment pipeline, thereby improving the development efficiency and code quality of the development team.

        Overall, JUnit is a powerful and flexible tool used to help developers write reliable, maintainable and high-quality unit tests. Using JUnit can improve code testability and stability, reduce potential bugs, and provide developers with fast feedback and confidence in their code.

2. How to use JUnit

        When using JUnit for unit testing, multiple test methods can be written to cover different functionality and scenarios. Here are some other examples of JUnit:

import org.junit.Assert;
import org.junit.Test;

public class ExampleTest {
    
    @Test
    public void testAssertEquals() {
        int expected = 5;
        int actual = 2 + 3;
        Assert.assertEquals(expected, actual);
    }
    
    @Test
    public void testAssertTrue() {
        boolean condition = true;
        Assert.assertTrue(condition);
    }
    
    @Test
    public void testAssertFalse() {
        boolean condition = false;
        Assert.assertFalse(condition);
    }
    
    @Test
    public void testAssertNull() {
        Object object = null;
        Assert.assertNull(object);
    }
    
    @Test
    public void testAssertNotNull() {
        Object object = new Object();
        Assert.assertNotNull(object);
    }
    
    @Test(expected = ArithmeticException.class)
    public void testException() {
        int result = 5 / 0;
    }
}

        In this example, we show the usage of some common JUnit assertion methods and annotations:

• Assert.assertEquals(expected, actual): Verify that two values ​​are equal.
• Assert.assertTrue(condition): Verify whether the given condition is true.
• Assert.assertFalse(condition): Verify whether the given condition is false.
• Assert.assertNull(object): Verify whether the given object is null.
• Assert.assertNotNull(object): Verify that the given object is not null.
• @TestAnnotation: used to mark a test method. JUnit will automatically look for @Testmethods marked with annotations and execute them.
• @Test(expected = Exception.class): Verify that the test method throws the expected exception.

        By writing test methods like the example above, you can write more unit tests to test different features and situations. These unit tests help you ensure that the expected behavior and logic of your methods are correct, and provide a reliable and fast way to verify your application during development.

3. JUnit simple example

        Suppose we have a Calculatorclass called which has a static method add()that adds two numbers and returns the result.

public class Calculator {
    public static int add(int a, int b) {
        return a + b;
    }
}

        We will use the JUnit framework for unit testing. build.gradleFirst, make sure that the JUnit dependency is introduced in the project file:

dependencies {
    // 其他依赖...
    testImplementation 'junit:junit:4.13.2'
}

        We then create a CalculatorTesttest class named that marks the test method with JUnit annotations and uses assertions to verify expected results.

import org.junit.Assert;
import org.junit.Test;

public class CalculatorTest {
    @Test
    public void testAdd() {
        int result = Calculator.add(2, 3);
        Assert.assertEquals(5, result);
    }
}

        In the above example, we use @Testthe annotation to mark a test method testAdd()that calls  Calculatorthe class's add()method and use Assert.assertEquals()assertions to verify that the results are as expected.

        Now, you can run this test class in Android Studio's test runner. Right-click CalculatorTestthe class and select "Run 'CalculatorTest'", or click the run button, and the unit test will be executed. If all goes well, you should see the test passed message.

4. Other scenes

        JUnit can handle a variety of complex testing scenarios. Actual unit testing scenarios and complexity will vary. But by using the JUnit framework and proper testing techniques, you can write more unit tests with comprehensive coverage to ensure the correctness of each module of the application.

Parametric testing

        Sometimes we need to perform multiple tests on the same test method using different parameters. JUnit supports parameterized testing through @ParameterizedTestannotations and annotations related to parameterized testing.@ValueSource

@ParameterizedTest
@ValueSource(ints = {1, 2, 3})
public void testSomeMethod(int value) {
    // 使用不同的参数执行测试
    // ...
}

Preparation and cleanup before and after testing

        Sometimes we need to do some preparation and cleanup work before and after executing the test, such as initializing a database connection or releasing resources. JUnit provides @BeforeEachand @AfterEachannotations to mark the code blocks that need to be executed before and after each test method is executed.

@BeforeEach
public void setUp() {
    // 执行测试前的准备工作
}

@AfterEach
public void tearDown() {
    // 执行测试后的清理工作
}

timeout test

        Sometimes we need to set the maximum running time of a certain test method and mark the test as failed after the timeout. JUnit @Timeout supports timeout testing through annotations.

@Test
@Timeout(value = 1000, unit = TimeUnit.MILLISECONDS)
public void testSomeMethod() {
    // 在1秒内执行测试，否则标记为失败
    // ...
}

Exception testing

        Sometimes we need to verify whether a method throws the expected exception. JUnit can use @Testannotated expectedproperties to mark expected exception types.

@Test(expected = ArithmeticException.class)
public void testDivisionByZero() {
    int result = 5 / 0;
}

Test sequence control

        Sometimes we need to execute test methods in a specified order, such as determining the execution order of certain test methods or creating test scenarios that depend on the results of other tests. JUnit 5 provides @TestMethodOrderannotations and @Orderannotations to control the execution order of test methods.

@TestMethodOrder(MethodOrderer.OrderAnnotation.class)
public class TestOrderExample {

    @Test
    @Order(1)
    public void testMethod1() {
        // 第一个测试方法
    }

    @Test
    @Order(2)
    public void testMethod2() {
        // 第二个测试方法
    }
}

        The above are just some examples of JUnit's complex scenarios. JUnit also provides more functions and extension points, such as parameter parsing, conditional testing, nested testing, etc., to adapt to different testing needs. Whether it is a simple basic test or a complex test scenario, JUnit can provide powerful and flexible support to help developers write comprehensive and reliable unit tests.