JUnit4-Description.java 源代码 解读与分析

JUnit4-Description.java源代码 解读与分析

作用域

1. children 子描述集合，套件测试时，children不为空，套件测试可以由套件测试和原子测试组合而成。
2. displayName 正常情况下，displayName格式都是这样的：方法名(类名)，方法formatDisplayName就是将其方法名，类名格式化成这种形式。
3. uniqueId 唯一标识符，从两个私有构造方法可看出，不对其设置的话，默认为displayName
4. annotation[] 注解
5. testClass 测试类

创建

由于构造方法私有化，Description的创建只能够通过静态方法来创建。

     public static Description createSuiteDescription(String name, Annotation... annotations) {
        return new Description(null, name, annotations);
    }

    public static Description createSuiteDescription(String name, Serializable uniqueId, Annotation... annotations) {
        return new Description(null, name, uniqueId, annotations);
    }
    public static Description createTestDescription(String className, String name, Annotation... annotations) {
        return new Description(null, formatDisplayName(name, className), annotations);
    }

    public static Description createTestDescription(Class<?> clazz, String name, Annotation... annotations) {
        return new Description(clazz, formatDisplayName(name, clazz.getName()), annotations);
    }

    public static Description createTestDescription(Class<?> clazz, String name) {
        return new Description(clazz, formatDisplayName(name, clazz.getName()));
    }

    public static Description createTestDescription(String className, String name, Serializable uniqueId) {
        return new Description(null, formatDisplayName(name, className), uniqueId);
    }

    public static Description createSuiteDescription(Class<?> testClass) {
        return new Description(testClass, testClass.getName(), testClass.getAnnotations());
    }

方法解读

源码中，有些方法有点不好理解，这次说明一下:
1.从当前注解数组中，获取某种类型的注解.
这个方法在JUnit中涉及到注解时，就常常出现。如作用域上的注解，方法上的注解啊，测试类上的注解啊…泛型T, 继承Annotation，即T是注解类型。Class.cast(Annotation)能够将Annotation转化为T类型

    public <T extends Annotation> T getAnnotation(Class<T> annotationType) {
        for (Annotation each : fAnnotations) {
            if (each.annotationType().equals(annotationType)) {
                return annotationType.cast(each); //相当于(T)each
            }
        }
        return null;
    }

2.获取测试类，测试类名，方法名时，这些信息都可为空，而实际上可能不为空，创建时，没有传进这些参数；但有一个信息不为空，那就是displayName, 它的格式是 方法名(类全名)
因此，在一些信息为空时，采取正则表达式匹配的方法，从displayName获取信息。
正则表达式中, 组是用括号划分的正则表达式，([\\s\\S]*)\\((.*)\\)中，第0组是整个表达式，第1组是[\\s\\S]*表示方法名, 第二组是.*，表示类全名。在下面方法中，如果匹配的话(matcher.matches()), 那么就会根据组数group来获取对应的信息。

    private static final Pattern METHOD_AND_CLASS_NAME_PATTERN = Pattern
            .compile("([\\s\\S]*)\\((.*)\\)");

    private String methodAndClassNamePatternGroupOrDefault(int group,
            String defaultString) {
        Matcher matcher = METHOD_AND_CLASS_NAME_PATTERN.matcher(toString());
        return matcher.matches() ? matcher.group(group) : defaultString;
    }

//获取方法名 group = 1
public String getMethodName() {
        return methodAndClassNamePatternGroupOrDefault(1, null);
    }

//获取类名， testClass不为空时，直接getName()获取，否则group=2
    public String getClassName() {
        return fTestClass != null ? fTestClass.getName() : methodAndClassNamePatternGroupOrDefault(2, toString());
    }

//获取测试类时，testClass为空时，尝试根据className, 使用Class.forName()获取
    public Class<?> getTestClass() {
        if (fTestClass != null) {
            return fTestClass;
        }
        String name = getClassName();
        if (name == null) {
            return null;
        }
        try {
            fTestClass = Class.forName(name, false, getClass().getClassLoader());
            return fTestClass;
        } catch (ClassNotFoundException e) {
            return null;
        }
    }

JUnit4中的使用

首先是抽象类Runner实现了Describable接口，使我们的运行类可被描述

public abstract class Runner implements Describable {
    public abstract Description getDescription();
    public abstract void run(RunNotifier notifier);
    public int testCount() {
        return getDescription().testCount();
    }

然后是ParentRunner(怎么称呼这个类，是真的不好表达，但它又很重要(=@__@=))。为其子类Runner，提供了许多方法。
而子类需要对自己子节点进行描述。（这里不详细讲，后面会有补充）

/**
 * Provides most of the functionality specific to a Runner that implements a
 * "parent node" in the test tree, with children defined by objects of some data
 * type {@code T}. (For {@link BlockJUnit4ClassRunner}, {@code T} is
 * {@link Method} . For {@link Suite}, {@code T} is {@link Class}.) Subclasses
 * must implement finding the children of the node, describing each child, and
 * running each child. ParentRunner will filter and sort children, handle
 * {@code @BeforeClass} and {@code @AfterClass} methods,
 * handle annotated {@link ClassRule}s, create a composite
 * {@link Description}, and run children sequentially.
 *
 * @since 4.5
 */
public abstract class ParentRunner<T> extends Runner{
    @Override
    public Description getDescription() {
        Description description = Description.createSuiteDescription(getName(),
                getRunnerAnnotations());
        for (T child : getFilteredChildren()) {
            description.addChild(describeChild(child));
        }
        return description;
    }

    protected abstract Description describeChild(T child);
}

如下是它的两个节点类型不同的子类:
以方法为测试节点 BlockJUnit4ClassRunner

public class BlockJUnit4ClassRunner extends ParentRunner<FrameworkMethod> {
    @Override
    protected Description describeChild(FrameworkMethod method) {
        Description description = methodDescriptions.get(method);

        if (description == null) {
            description = Description.createTestDescription(getTestClass().getJavaClass(),
                    testName(method), method.getAnnotations());
            methodDescriptions.putIfAbsent(method, description);
        }

        return description;
    }
}

以Runner为节点的 Suite套件测试

public class Suite extends ParentRunner<Runner> {
    @Override
    protected Description describeChild(Runner child) {
        return child.getDescription();
    }
}

完整代码

package org.junit.runner;

import java.io.Serializable;
import java.lang.annotation.Annotation;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * A <code>Description</code> describes a test which is to be run or has been run. <code>Descriptions</code>
 * can be atomic (a single test) or compound (containing children tests). <code>Descriptions</code> are used
 * to provide feedback about the tests that are about to run (for example, the tree view
 * visible in many IDEs) or tests that have been run (for example, the failures view).
 * <p>
 * <code>Descriptions</code> are implemented as a single class rather than a Composite because
 * they are entirely informational. They contain no logic aside from counting their tests.
 * <p>
 * In the past, we used the raw {@link junit.framework.TestCase}s and {@link junit.framework.TestSuite}s
 * to display the tree of tests. This was no longer viable in JUnit 4 because atomic tests no longer have
 * a superclass below {@link Object}. We needed a way to pass a class and name together. Description
 * emerged from this.
 *
 * @see Request
 * @see Runner
 * @since 4.0
 */
public class Description implements Serializable {
    private static final long serialVersionUID = 1L;

    private static final Pattern METHOD_AND_CLASS_NAME_PATTERN = Pattern
            .compile("([\\s\\S]*)\\((.*)\\)");

    /**
     * Create a <code>Description</code> named <code>name</code>.
     * Generally, you will add children to this <code>Description</code>.
     *
     * @param name the name of the <code>Description</code>
     * @param annotations meta-data about the test, for downstream interpreters
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createSuiteDescription(String name, Annotation... annotations) {
        return new Description(null, name, annotations);
    }

    /**
     * Create a <code>Description</code> named <code>name</code>.
     * Generally, you will add children to this <code>Description</code>.
     *
     * @param name the name of the <code>Description</code>
     * @param uniqueId an arbitrary object used to define uniqueness (in {@link #equals(Object)}
     * @param annotations meta-data about the test, for downstream interpreters
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createSuiteDescription(String name, Serializable uniqueId, Annotation... annotations) {
        return new Description(null, name, uniqueId, annotations);
    }

    /**
     * Create a <code>Description</code> of a single test named <code>name</code> in the 'class' named
     * <code>className</code>. Generally, this will be a leaf <code>Description</code>. This method is a better choice
     * than {@link #createTestDescription(Class, String, Annotation...)} for test runners whose test cases are not
     * defined in an actual Java <code>Class</code>.
     *
     * @param className the class name of the test
     * @param name the name of the test (a method name for test annotated with {@link org.junit.Test})
     * @param annotations meta-data about the test, for downstream interpreters
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createTestDescription(String className, String name, Annotation... annotations) {
        return new Description(null, formatDisplayName(name, className), annotations);
    }

    /**
     * Create a <code>Description</code> of a single test named <code>name</code> in the class <code>clazz</code>.
     * Generally, this will be a leaf <code>Description</code>.
     *
     * @param clazz the class of the test
     * @param name the name of the test (a method name for test annotated with {@link org.junit.Test})
     * @param annotations meta-data about the test, for downstream interpreters
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createTestDescription(Class<?> clazz, String name, Annotation... annotations) {
        return new Description(clazz, formatDisplayName(name, clazz.getName()), annotations);
    }

    /**
     * Create a <code>Description</code> of a single test named <code>name</code> in the class <code>clazz</code>.
     * Generally, this will be a leaf <code>Description</code>.
     * (This remains for binary compatibility with clients of JUnit 4.3)
     *
     * @param clazz the class of the test
     * @param name the name of the test (a method name for test annotated with {@link org.junit.Test})
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createTestDescription(Class<?> clazz, String name) {
        return new Description(clazz, formatDisplayName(name, clazz.getName()));
    }

    /**
     * Create a <code>Description</code> of a single test named <code>name</code> in the class <code>clazz</code>.
     * Generally, this will be a leaf <code>Description</code>.
     *
     * @param name the name of the test (a method name for test annotated with {@link org.junit.Test})
     * @return a <code>Description</code> named <code>name</code>
     */
    public static Description createTestDescription(String className, String name, Serializable uniqueId) {
        return new Description(null, formatDisplayName(name, className), uniqueId);
    }

    private static String formatDisplayName(String name, String className) {
        return String.format("%s(%s)", name, className);
    }

    /**
     * Create a <code>Description</code> named after <code>testClass</code>
     *
     * @param testClass A {@link Class} containing tests
     * @return a <code>Description</code> of <code>testClass</code>
     */
    public static Description createSuiteDescription(Class<?> testClass) {
        return new Description(testClass, testClass.getName(), testClass.getAnnotations());
    }

    /**
     * Describes a Runner which runs no tests
     */
    public static final Description EMPTY = new Description(null, "No Tests");

    /**
     * Describes a step in the test-running mechanism that goes so wrong no
     * other description can be used (for example, an exception thrown from a Runner's
     * constructor
     */
    public static final Description TEST_MECHANISM = new Description(null, "Test mechanism");

    /*
     * We have to use the f prefix until the next major release to ensure
     * serialization compatibility. 
     * See https://github.com/junit-team/junit/issues/976
     */
    private final Collection<Description> fChildren = new ConcurrentLinkedQueue<Description>();
    private final String fDisplayName;
    private final Serializable fUniqueId;
    private final Annotation[] fAnnotations;
    private volatile /* write-once */ Class<?> fTestClass;

    private Description(Class<?> clazz, String displayName, Annotation... annotations) {
        this(clazz, displayName, displayName, annotations);
    }

    private Description(Class<?> testClass, String displayName, Serializable uniqueId, Annotation... annotations) {
        if ((displayName == null) || (displayName.length() == 0)) {
            throw new IllegalArgumentException(
                    "The display name must not be empty.");
        }
        if ((uniqueId == null)) {
            throw new IllegalArgumentException(
                    "The unique id must not be null.");
        }
        this.fTestClass = testClass;
        this.fDisplayName = displayName;
        this.fUniqueId = uniqueId;
        this.fAnnotations = annotations;
    }

    /**
     * @return a user-understandable label
     */
    public String getDisplayName() {
        return fDisplayName;
    }

    /**
     * Add <code>Description</code> as a child of the receiver.
     *
     * @param description the soon-to-be child.
     */
    public void addChild(Description description) {
        fChildren.add(description);
    }

    /**
     * Gets the copy of the children of this {@code Description}.
     * Returns an empty list if there are no children.
     */
    public ArrayList<Description> getChildren() {
        return new ArrayList<Description>(fChildren);
    }

    /**
     * @return <code>true</code> if the receiver is a suite
     */
    public boolean isSuite() {
        return !isTest();
    }

    /**
     * @return <code>true</code> if the receiver is an atomic test
     */
    public boolean isTest() {
        return fChildren.isEmpty();
    }

    /**
     * @return the total number of atomic tests in the receiver
     */
    public int testCount() {
        if (isTest()) {
            return 1;
        }
        int result = 0;
        for (Description child : fChildren) {
            result += child.testCount();
        }
        return result;
    }

    @Override
    public int hashCode() {
        return fUniqueId.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (!(obj instanceof Description)) {
            return false;
        }
        Description d = (Description) obj;
        return fUniqueId.equals(d.fUniqueId);
    }

    @Override
    public String toString() {
        return getDisplayName();
    }

    /**
     * @return true if this is a description of a Runner that runs no tests
     */
    public boolean isEmpty() {
        return equals(EMPTY);
    }

    /**
     * @return a copy of this description, with no children (on the assumption that some of the
     *         children will be added back)
     */
    public Description childlessCopy() {
        return new Description(fTestClass, fDisplayName, fAnnotations);
    }

    /**
     * @return the annotation of type annotationType that is attached to this description node,
     *         or null if none exists
     */
    public <T extends Annotation> T getAnnotation(Class<T> annotationType) {
        for (Annotation each : fAnnotations) {
            if (each.annotationType().equals(annotationType)) {
                return annotationType.cast(each);
            }
        }
        return null;
    }

    /**
     * @return all of the annotations attached to this description node
     */
    public Collection<Annotation> getAnnotations() {
        return Arrays.asList(fAnnotations);
    }

    /**
     * @return If this describes a method invocation,
     *         the class of the test instance.
     */
    public Class<?> getTestClass() {
        if (fTestClass != null) {
            return fTestClass;
        }
        String name = getClassName();
        if (name == null) {
            return null;
        }
        try {
            fTestClass = Class.forName(name, false, getClass().getClassLoader());
            return fTestClass;
        } catch (ClassNotFoundException e) {
            return null;
        }
    }

    /**
     * @return If this describes a method invocation,
     *         the name of the class of the test instance
     */
    public String getClassName() {
        return fTestClass != null ? fTestClass.getName() : methodAndClassNamePatternGroupOrDefault(2, toString());
    }

    /**
     * @return If this describes a method invocation,
     *         the name of the method (or null if not)
     */
    public String getMethodName() {
        return methodAndClassNamePatternGroupOrDefault(1, null);
    }

    private String methodAndClassNamePatternGroupOrDefault(int group,
            String defaultString) {
        Matcher matcher = METHOD_AND_CLASS_NAME_PATTERN.matcher(toString());
        return matcher.matches() ? matcher.group(group) : defaultString;
    }
}