摘要：前言在上次的博客中我們提到了最終由以為參數(shù)執(zhí)行測(cè)試樣例，但并沒(méi)有解釋到底測(cè)試方法是如何被運(yùn)行起來(lái)的，一些諸如之類的特性又到底是如何實(shí)現(xiàn)的呢。這次我們就集中深入的運(yùn)行機(jī)制來(lái)探究樣例是如何被運(yùn)行的。使用拿到的直接運(yùn)行方法。

在上次的博客中我們提到了最終由Runner以Notifier為參數(shù)執(zhí)行測(cè)試樣例，但并沒(méi)有解釋到底測(cè)試方法是如何被運(yùn)行起來(lái)的，一些諸如RunWith、RunAfter之類的特性又到底是如何實(shí)現(xiàn)的呢。這次我們就集中深入Runner的運(yùn)行機(jī)制來(lái)探究樣例是如何被運(yùn)行的。

首先我們需要把注解等用戶配置信息收集起來(lái)并attach到對(duì)應(yīng)的方法、類和屬性上，為了在之后的代碼中能夠方便的取到這些信息，我們要包裝原有的類、方法和域，分別如下。

TestClass包含原有的clazz信息，并且維護(hù)了兩個(gè)Map來(lái)管理它所包含的方法與屬性，每個(gè)map的鍵是注解，而值是標(biāo)上注解的FrameWorkMethod或FrameWorkField。同時(shí)TestClass還默認(rèn)內(nèi)置兩個(gè)Comparator來(lái)排序自己所包含的方法和屬性。

下面給出如何構(gòu)造一個(gè)TestClass的代碼。

public TestClass(Class clazz) {
        this.clazz = clazz;
        if (clazz != null && clazz.getConstructors().length > 1) {
            throw new IllegalArgumentException(
                    "Test class can only have one constructor");
        }

        Map, List> methodsForAnnotations =
                new LinkedHashMap, List>();
        Map, List> fieldsForAnnotations =
                new LinkedHashMap, List>();

        scanAnnotatedMembers(methodsForAnnotations, fieldsForAnnotations);

        this.methodsForAnnotations = makeDeeplyUnmodifiable(methodsForAnnotations);
        this.fieldsForAnnotations = makeDeeplyUnmodifiable(fieldsForAnnotations);
    }

    protected void scanAnnotatedMembers(Map, List> methodsForAnnotations, Map, List> fieldsForAnnotations) {
        for (Class eachClass : getSuperClasses(clazz)) {
            for (Method eachMethod : MethodSorter.getDeclaredMethods(eachClass)) {
                addToAnnotationLists(new FrameworkMethod(eachMethod), methodsForAnnotations);
            }
            // ensuring fields are sorted to make sure that entries are inserted
            // and read from fieldForAnnotations in a deterministic order
            for (Field eachField : getSortedDeclaredFields(eachClass)) {
                addToAnnotationLists(new FrameworkField(eachField), fieldsForAnnotations);
            }
        }
    }

TestClass的主要功能就是向Runner提供clazz信息以及附帶的注解信息，上文的addToAnnotationLists將對(duì)應(yīng)member加入該annotation映射的member列表。下面給一個(gè)TestClass的方法列表截圖，大家可以感受一下。

我們先給出它的父類FrameWorkMember的定義

public abstract class FrameworkMember> implements
        Annotatable {
    abstract boolean isShadowedBy(T otherMember);

    boolean isShadowedBy(List members) {
        for (T each : members) {
            if (isShadowedBy(each)) {
                return true;
            }
        }
        return false;
    }

    protected abstract int getModifiers();

    /**
     * Returns true if this member is static, false if not.
     */
    public boolean isStatic() {
        return Modifier.isStatic(getModifiers());
    }

    /**
     * Returns true if this member is public, false if not.
     */
    public boolean isPublic() {
        return Modifier.isPublic(getModifiers());
    }

    public abstract String getName();

    public abstract Class getType();

    public abstract Class getDeclaringClass();
}

FrameWorkMethod包裝了方法信息以及方法相關(guān)的注解以及一些基本的驗(yàn)證方法比如validatePublicVoid和是否被其他FrameWorkMethod覆蓋的判斷方法，除父類要求外它主要提供的信息如下：

Annotations

Method

ReturnType

ParameterTypes

同F(xiàn)rameWorkMethod差不多，F(xiàn)rameWorkField和它繼承自同一父類，較為簡(jiǎn)單，此處就不再詳細(xì)介紹了。

Statement是最小的執(zhí)行單元，諸如RunAfter、RunWith等功能均是通過(guò)嵌套Statement來(lái)實(shí)現(xiàn)的，下面我們先給出Statement的定義，再給出一個(gè)嵌套的例子。

public abstract class Statement {
    /**
     * Run the action, throwing a {@code Throwable} if anything goes wrong.
     */
    public abstract void evaluate() throws Throwable;
}

下面以RunAfter的實(shí)現(xiàn)為例來(lái)說(shuō)明：

public class RunAfters extends Statement {
   private final Statement next;

   private final Object target;

   private final List afters;

   public RunAfters(Statement next, List afters, Object target) {
       this.next = next;
       this.afters = afters;
       this.target = target;
   }

   @Override
   public void evaluate() throws Throwable {
       List errors = new ArrayList();
       try {
           next.evaluate();
       } catch (Throwable e) {
           errors.add(e);
       } finally {
           for (FrameworkMethod each : afters) {
               try {
                   each.invokeExplosively(target);
               } catch (Throwable e) {
                   errors.add(e);
               }
           }
       }
       MultipleFailureException.assertEmpty(errors);
   }
}

可以看出新的Statement執(zhí)行時(shí)會(huì)先執(zhí)行舊有的Statement，再將附加上的一系列方法以target為參數(shù)運(yùn)行。

Junit使用虛類ParentRunner來(lái)管理復(fù)合的Runner，使用composite模式，而B(niǎo)lockJunitClassRunner是ParentRunner的一個(gè)子類，主要負(fù)責(zé)同一測(cè)試類多個(gè)方法的組合測(cè)試，也就是最常用的情形。我們首先還是聚焦在如何運(yùn)行測(cè)試樣例上。

首先看ParentRunner如何實(shí)現(xiàn)run方法

@Override
    public void run(final RunNotifier notifier) {
        EachTestNotifier testNotifier = new EachTestNotifier(notifier,
                getDescription());
        try {
            Statement statement = classBlock(notifier);
            statement.evaluate();
        } catch (AssumptionViolatedException e) {
            testNotifier.addFailedAssumption(e);
        } catch (StoppedByUserException e) {
            throw e;
        } catch (Throwable e) {
            testNotifier.addFailure(e);
        }
    }

這里有個(gè)classBlock方法用來(lái)提供真正運(yùn)行的Statement，下面我們看一看

protected Statement classBlock(final RunNotifier notifier) {
        Statement statement = childrenInvoker(notifier);
        if (!areAllChildrenIgnored()) {
            statement = withBeforeClasses(statement);
            statement = withAfterClasses(statement);
            statement = withClassRules(statement);
        }
        return statement;
    }

這個(gè)過(guò)程就是先通過(guò)反射獲得初始Statement，然后附加上RunBefore、RunAfter、用戶自定義Rule，我們來(lái)看一下初始Statement是如何生成的。

其過(guò)程是先取得所有通過(guò)過(guò)濾器的Childeren，再使用內(nèi)置的調(diào)度器來(lái)分別按順序調(diào)用runChild方法，下面我們給出BlockJunit4ClassRunner的runChild方法

@Override
    protected void runChild(final FrameworkMethod method, RunNotifier notifier) {
        Description description = describeChild(method);
        if (isIgnored(method)) {
            notifier.fireTestIgnored(description);
        } else {
            Statement statement;
            try {
                statement = methodBlock(method);
            }
            catch (Throwable ex) {
                statement = new Fail(ex);
            }
            runLeaf(statement, description, notifier);
        }
    }

這里面最重要的就是RunLeaf也就是原子測(cè)試方法以及如何為單個(gè)方法生成的Statement——methodBlock，我們?cè)谙旅娣謩e給出。

protected final void runLeaf(Statement statement, Description description,
            RunNotifier notifier) {
        EachTestNotifier eachNotifier = new EachTestNotifier(notifier, description);
        eachNotifier.fireTestStarted();
        try {
            statement.evaluate();
        } catch (AssumptionViolatedException e) {
            eachNotifier.addFailedAssumption(e);
        } catch (Throwable e) {
            eachNotifier.addFailure(e);
        } finally {
            eachNotifier.fireTestFinished();
        }
    }

RunLeaf的邏輯并不難，先通知Notifier測(cè)試開(kāi)始，再直接調(diào)用statement的evaluate方法，最后通知Notifier測(cè)試結(jié)束。我們?cè)賮?lái)看看statement是如何生成的。

protected Statement methodBlock(final FrameworkMethod method) {
        Object test;
        try {
            test = new ReflectiveCallable() {
                @Override
                protected Object runReflectiveCall() throws Throwable {
                    return createTest(method);
                }
            }.run();
        } catch (Throwable e) {
            return new Fail(e);
        }

        Statement statement = methodInvoker(method, test);
        statement = possiblyExpectingExceptions(method, test, statement);
        statement = withPotentialTimeout(method, test, statement);
        statement = withBefores(method, test, statement);
        statement = withAfters(method, test, statement);
        statement = withRules(method, test, statement);
        return statement;
    }

上述代碼的邏輯還是比較復(fù)雜的，這里簡(jiǎn)單概述一下，首先構(gòu)造測(cè)試類的實(shí)例，然后為對(duì)應(yīng)method構(gòu)造statement的子類InvokeMethod，然后調(diào)用FrameWorkMethod的反射運(yùn)行方法，如下：

public class InvokeMethod extends Statement {
    private final FrameworkMethod testMethod;
    private final Object target;

    public InvokeMethod(FrameworkMethod testMethod, Object target) {
        this.testMethod = testMethod;
        this.target = target;
    }

    @Override
    public void evaluate() throws Throwable {
        testMethod.invokeExplosively(target);
    }
}

Suite是對(duì)于ParentRunner的另一子類實(shí)現(xiàn)，主要用于多個(gè)測(cè)試類的情形。Suite自己維護(hù)一個(gè)runner列表，實(shí)現(xiàn)了getChilderen方法，其層次是在上文中提到的runChildren里，這一部分需要取出children節(jié)點(diǎn)然后調(diào)用runChild方法。我們著重考察suite和BlockJunit4ClassRunner在getChildren和runChild方法上的區(qū)別。Suite通過(guò)用戶傳入的runnerBuilder為每個(gè)類多帶帶建立runner作為children返回，而后者則返回帶Test注解的FrameWorkMethod列表。使用getChildren拿到的runner直接運(yùn)行run方法。下面我們給出RunnerBuilder是如何為一系列測(cè)試類提供一系列對(duì)應(yīng)的Runner，說(shuō)來(lái)也簡(jiǎn)單，就是使用為單個(gè)類建立Runner的方法為每個(gè)測(cè)試類建立最后組成一個(gè)集合。但是此處需要防止遞歸——this builder will throw an exception if it is requested for another runner for {@code parent} before this call completes（說(shuō)實(shí)話這段如何防止遞歸我也沒(méi)看懂，有看懂的兄弟求教）。對(duì)于Suite而言，一般就是它維護(hù)一個(gè)BlockJUnit4ClassRunner列表。

public abstract class RunnerBuilder {
    private final Set> parents = new HashSet>();

    /**
     * Override to calculate the correct runner for a test class at runtime.
     *
     * @param testClass class to be run
     * @return a Runner
     * @throws Throwable if a runner cannot be constructed
     */
    public abstract Runner runnerForClass(Class testClass) throws Throwable;

    /**
     * Always returns a runner, even if it is just one that prints an error instead of running tests.
     *
     * @param testClass class to be run
     * @return a Runner
     */
    public Runner safeRunnerForClass(Class testClass) {
        try {
            return runnerForClass(testClass);
        } catch (Throwable e) {
            return new ErrorReportingRunner(testClass, e);
        }
    }

    Class addParent(Class parent) throws InitializationError {
        if (!parents.add(parent)) {
            throw new InitializationError(String.format("class "%s" (possibly indirectly) contains itself as a SuiteClass", parent.getName()));
        }
        return parent;
    }

    void removeParent(Class klass) {
        parents.remove(klass);
    }

    /**
     * Constructs and returns a list of Runners, one for each child class in
     * {@code children}.  Care is taken to avoid infinite recursion:
     * this builder will throw an exception if it is requested for another
     * runner for {@code parent} before this call completes.
     */
    public List runners(Class parent, Class[] children)
            throws InitializationError {
        addParent(parent);

        try {
            return runners(children);
        } finally {
            removeParent(parent);
        }
    }

    public List runners(Class parent, List> children)
            throws InitializationError {
        return runners(parent, children.toArray(new Class[0]));
    }

    private List runners(Class[] children) {
        List runners = new ArrayList();
        for (Class each : children) {
            Runner childRunner = safeRunnerForClass(each);
            if (childRunner != null) {
                runners.add(childRunner);
            }
        }
        return runners;
    }
}

Junit使用BlockJUnit4ClassRunnerWithParameters繼承BlockJUnit4ClassRunner來(lái)完成對(duì)于組合方法的帶參數(shù)測(cè)試。它覆寫(xiě)了createTest方法和對(duì)構(gòu)造器和域的驗(yàn)證方法。

@Override
    public Object createTest() throws Exception {
        InjectionType injectionType = getInjectionType();
        switch (injectionType) {
            case CONSTRUCTOR:
                return createTestUsingConstructorInjection();
            case FIELD:
                return createTestUsingFieldInjection();
            default:
                throw new IllegalStateException("The injection type "
                        + injectionType + " is not supported.");
        }
    }

Parameterized繼承了Suite，用來(lái)完成對(duì)多個(gè)類的組合測(cè)試的帶參數(shù)版本。它提供三大注解——Parameters、Parameter、UseParametersRunnerFactory，前兩者是用來(lái)指定參數(shù)的，后者用來(lái)指定對(duì)于每一個(gè)測(cè)試類如何生成Runner的工廠,默認(rèn)工廠返回BlockJUnit4ClassRunnerWithParameters。我們下面給出內(nèi)置的工廠類如何創(chuàng)建runner的代碼。

        private List createRunnersForParameters(
                Iterable