断言 Assert.assertEquals（）

unit.framework包下的Assert提供了多个断言方法. 主用于比较测试传递进去的两个参数.

Assert.assertEquals();及其重载方法: 
1. 如果两者一致, 程序继续往下运行. 
2. 如果两者不一致, 中断测试方法, 抛出异常信息 AssertionFailedError .

查看源码, 以Assert.assertEquals(int expected, int actual)为例:

/**
 * Asserts that two ints are equal. 断言两个int是相等的
 */
static public void assertEquals(int expected, int actual) {
    assertEquals(null, expected, actual);
}
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可以看到里面调用了assertEquals(String message, int expected, int actual)方法:

/**
 * Asserts that two ints are equal. If they are not
 * an AssertionFailedError is thrown with the given message.
 * 如果不抛出带有 message 的异常(AssertionFailedError)信息, 则表明两者相等
 */
static public void assertEquals(String message, int expected, int actual) {
    assertEquals(message, Integer.valueOf(expected), Integer.valueOf(actual));
}
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可以看到, 这里把int类型封箱成为Integer类型. 注释说, 会抛异常, 但这里没有. 没关系, 我们接着看里面调用: assertEquals(String message, Object expected, Object actual)方法:

/**
 * Asserts that two objects are equal. If they are not
 * an AssertionFailedError is thrown with the given message.
 * 如果不抛出带有 message 的异常(AssertionFailedError)信息, 则表明两者相等(这里比较的是Object对象)
 */
static public void assertEquals(String message, Object expected, Object actual) {
    if (expected == null && actual == null) {
        return;
    }
    if (expected != null && expected.equals(actual)) {
        return;
    }
    failNotEquals(message, expected, actual);
}
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两个if语句, 判断了两者相等的情况: 引用(地址)相等或者内容相等. 如果这两种情况都不相等, 那么表明1参和2参实际是不相等, 所以基本可以判断出要抛出的异常肯定是在failNotEquals(String message, Object expected, Object actual)方法抛出的, 接下来就比较简单了:

static public void failNotEquals(String message, Object expected, Object actual) {
    fail(format(message, expected, actual));
}

public static String format(String message, Object expected, Object actual) {
    String formatted = "";
    if (message != null && message.length() > 0) {
        formatted = message + " ";
    }
    return formatted + "expected:<" + expected + "> but was:<" + actual + ">";
}
/**
* Fails a test with the given message.
*/
static public void fail(String message) {
    if (message == null) {
        throw new AssertionFailedError();
    }
    throw new AssertionFailedError(message);
}
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以上可以看出, 最终是由fail(String message)这个方法抛出异常信息!!

Assert.assertEquals()使用方法: 
使用, 示例代码:

Assert.assertEquals(true, arry.contains("hello"));
Assert.assertEquals(39991L, aa.getLong("key3", 0L));
Assert.assertEquals(true, bb.getBoolean("key4", false));
Assert.assertEquals(5.3f, cc.getFloat("key5", 0.f));
Assert.assertEquals(99, dd.getInt("key6", 1));
Assert.assertEquals("如果打印本信息, 证明参数不相等", 10L, 10);
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按照源码分析, 我们可以把一个预期结果作为1参传递进去. 2参传递我们需要测试的方法. 然后执行. 相等, 代码继续往下执行, 不相等, 中断执行, 抛出异常信息!!!

略作一提: 
Assert.assertSame(Object expected, Object actual)方法: 
查看源码, 其比较的是引用地址是否相等, 并没有对内容进行比较:

/**
 * Asserts that two objects refer to the same object. If they are not
 * the same an AssertionFailedError is thrown.
 */
static public void assertSame(Object expected, Object actual) {
    assertSame(null, expected, actual);
}
/**
 * Asserts that two objects refer to the same object. If they are not
 * an AssertionFailedError is thrown with the given message.
 */
static public void assertSame(String message, Object expected, Object actual) {
    if (expected == actual) {
        return;
    }
    failNotSame(message, expected, actual);
}
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原文：https://blog.csdn.net/tgvincent/article/details/81296349