测试驱动开发(Test-Driven Development)。是敏捷开发中的一项核心实践和技术。

TDD是在开发功能代码之前，先编写单元测试用例代码，测试代码确定需要编写什么产品代码。

变红 ——> 变绿  ——>  重构

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在进行 TDD 案例编写的时候，看一个简单的需求（经典案例）：

• 输入一个非元音字符，并预期返回字符本身
• 输入一个元音（a,e,i,o,u），返回  mommy
• 输入一个元音超过字符串的30%，被 mommy 替换
• 输入一个元音超过30%，并且存在连续元音的字符串，并预期只被替换一次

————>   "hmm" will become "hmm" (no vowels)

————>   "his" will become "hmommys" (vowels are more than 30%)

————>   "hear" will become "hmommyr" and not "hmommymommyr" (continuous set of vowels)

如果直接进行代码编写，靠大脑分析分析整理代码的逻辑，和书写步骤的时候比较繁琐。

那么接下来就看下这个案例在 TDD 中如何逐步成型的吧。

第一次：首先编写测试用例代码，运行。结果变红。

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}public String tddTest(String inputStr){return null;
}---> java.lang.AssertionError: expected:<h> but was:<null>

 编写逻辑代码，结果变绿

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}public String tddTest(String inputStr){return inputStr;
}

第二次：加入新的业务逻辑（输入元音字母 返回特定的字符串）运行结果变红

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}@Test
public void testVowel(){String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("mommy", result);
}public String tddTest(String inputStr){return inputStr;
}

编写业务逻辑代码运行 

@Test
public void test(){String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}public String tddTest(String inputStr){List<String> vowelList = Arrays.asList("a","e","i","o","u");if(vowelList.contains(inputStr)){return "mommy";}else{return inputStr;}
}

 修改测试用例代码后 变绿

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}@Test
public void testVowel(){String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("mommy", result);
}public String tddTest(String inputStr){List<String> vowelList = Arrays.asList("a","e","i","o","u");if(vowelList.contains(inputStr)){return "mommy";}else{return inputStr;}
}

第三次：加入新的业务逻辑（元音字符超过字符串的 30% ，被特定字符串替换）运行结果变红

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}@Test
public void testVowel(){String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("mommy", result);
}@Test
public void testVowelMore30PercentInStr(){String inputStr = "ab";String result = tddTest(inputStr);Assert.assertEquals("mommyb", result);
}public String tddTest(String inputStr){List<String> vowelList = Arrays.asList("a","e","i","o","u");if(vowelList.contains(inputStr)){return "mommy";}else{return inputStr;}
}

编写业务逻辑代码 测试后变绿

@Test
public void test(){String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);
}@Test
public void testVowel(){String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("mommy", result);
}@Test
public void testVowelMore30PercentInStr(){String inputStr = "ab";String result = tddTest(inputStr);Assert.assertEquals("mommyb", result);
}public String tddTest(String inputStr){List<String> vowelList = Arrays.asList("a","e","i","o","u");char[] charArray = inputStr.toCharArray();int sum = 0;String vowelStr = "aeiou";String str = "";if(inputStr.length() == 1 ){if(vowelList.contains(inputStr)){return "mommy";}else{return inputStr;}}else if(inputStr.length() > 1){for (char c : charArray) {if(vowelStr.indexOf(c) > 0){sum += 1;}}if((float)sum/(float)charArray.length >= 0.3){for (char c : charArray) {if(vowelStr.indexOf(c) > 0){str += "mommy";}else{str += c;}}}return str;}else{return null;}
}

重构代码

首先 ：
{List<String> vowelList = Arrays.asList("a","e","i","o","u");vowelList.contains(inputStr)
}
这部分代码和
{String vowelStr = "aeiou";char[] charArray = inputStr.toCharArray();vowelStr.indexOf(inputStr) >= 0
}
在功能上有重复性，根据情况进行合理的取舍（因为在传入的是字符串的时候，
判断元音字符的占比等需要更多的代码处理），决定采用下面的部分。
并进行方法抽取
{private static boolean validVowelIsExist(String vowelStr, char c) {return vowelStr.indexOf(c) > 0;}
}其次 ：计算元音在字符传中的数量，是一个独立的逻辑，可以进行方法抽取
{for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {sum += 1;}}
}
————>
{private int getVowelCountInStr(char[] charArray, int sum, String vowelStr) {for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {sum += 1;}}return sum;}
}再次 ：也可以对元音替换方法进行抽取
{private static String replaceVowelWithConstant(char[] charArray, String vowelStr, String str) {for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {str += REPLACE_CONSTANT;} else {str += c;}}return str;}
}最后 : 对数字和字符串进行定义常量
{private final static double VOWEL_PERCENT = 0.3;private final static String REPLACE_CONSTANT = "mommy";
}

 重构后的代码则是

    private final static double VOWEL_PERCENT = 0.3;private final static String REPLACE_CONSTANT = "mommy";public String tddTest(String inputStr) {char[] charArray = inputStr.toCharArray();int sum = 0;String vowelStr = "aeiou";String str = "";if (inputStr.length() > 0) {sum = getVowelCountInStr(charArray, sum, vowelStr);boolean falg = JudgeVowelPercentInStr(charArray, sum);if (falg) {str = replaceVowelWithConstant(charArray, vowelStr, str);}else {return inputStr;}return str;} else {return null;}}private static String replaceVowelWithConstant(char[] charArray, String vowelStr, String str) {for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {str += REPLACE_CONSTANT;} else {str += c;}}return str;}private boolean JudgeVowelPercentInStr(char[] charArray, int sum) {return (float) sum / (float) charArray.length >= VOWEL_PERCENT;}private int getVowelCountInStr(char[] charArray, int sum, String vowelStr) {for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {sum += 1;}}return sum;}private static boolean validVowelIsExist(String vowelStr, char c) {return vowelStr.indexOf(c) >= 0;}

第三次：加入新的业务逻辑（连续元音的字符串，并预期只被替换一次）运行结果变红

@Test
public void testContinuousVowelMore30PercentInStr() {String inputStr = "fjdsooewqe";String result = tddTest(inputStr);Assert.assertEquals("fjdsmommywqmommy", result);
}

修改业务逻辑，由于对元音替换我们前面已经进行了方法抽取，所以没必要在主方法中进行修改开发。修改后测试变绿

private static String replaceVowelWithConstant(char[] charArray, String vowelStr, String str) {for (int i = 0; i < charArray.length; i++) {if (validVowelIsExist(vowelStr, charArray[i])) {if (i == 0) {if (!validVowelIsExist(vowelStr, charArray[i + 1])) {str += REPLACE_CONSTANT;}} else {if (!validVowelIsExist(vowelStr, charArray[i - 1])) {str += REPLACE_CONSTANT;}}} else {str += charArray[i];}}return str;
}

自此，开发基本完成，我又对多种情况的可能性，进尽可能的减少，行了进一步的修改和完善，使得 bug 数量以及后续的维护尽可能的减少。其中可能存在大量的不完美的代码和不健全的业务逻辑，如果读者有发现可以和我提出来，尽可能的改善。

完整代码

import org.junit.Assert;
import org.junit.Test;import com.aia.common.base.TestBase;public class TDDtest extends TestBase {private final static double VOWEL_PERCENT = 0.3;private final static String REPLACE_CONSTANT = "mommy";@Testpublic void test() {String inputStr = "h";String result = tddTest(inputStr);Assert.assertEquals("h", result);}@Testpublic void testParamIsNull() {String inputStr = "";String result = tddTest(inputStr);Assert.assertEquals(null, result);}@Testpublic void testVowel() {String inputStr = "a";String result = tddTest(inputStr);Assert.assertEquals("mommy", result);}@Testpublic void testVowelMore30PercentInStr() {String inputStr = "ab";String result = tddTest(inputStr);Assert.assertEquals("mommyb", result);}@Testpublic void testContinuousVowelMore30PercentInStr() {String inputStr = "fjdsooewqe";String result = tddTest(inputStr);Assert.assertEquals("fjdsmommywqmommy", result);}@Testpublic void testContinuousVowelMore30PercentInStr2() {String inputStr = "afjdsooewqe";String result = tddTest(inputStr);Assert.assertEquals("mommyfjdsmommywqmommy", result);}public String tddTest(String inputStr) {char[] charArray = inputStr.toCharArray();int sum = 0;String vowelStr = "aeiou";String str = "";if (inputStr.length() == 1) {if (validVowelIsExist(vowelStr, charArray[0])) {return REPLACE_CONSTANT;} else {return inputStr;}} else if (inputStr.length() > 1) {sum = getVowelCountInStr(charArray, sum, vowelStr);if (JudgeVowelPercentInStr(charArray, sum)) {str = replaceVowelWithConstant(charArray, vowelStr, str);}} else {return null;}return str;}private static String replaceVowelWithConstant(char[] charArray, String vowelStr, String str) {for (int i = 0; i < charArray.length; i++) {if (validVowelIsExist(vowelStr, charArray[i])) {if (i == 0) {if (!validVowelIsExist(vowelStr, charArray[i + 1])) {str += REPLACE_CONSTANT;}} else {if (!validVowelIsExist(vowelStr, charArray[i - 1])) {str += REPLACE_CONSTANT;}}} else {str += charArray[i];}}return str;}private boolean JudgeVowelPercentInStr(char[] charArray, int sum) {return (float) sum / (float) charArray.length >= VOWEL_PERCENT;}private int getVowelCountInStr(char[] charArray, int sum, String vowelStr) {for (char c : charArray) {if (validVowelIsExist(vowelStr, c)) {sum += 1;}}return sum;}private static boolean validVowelIsExist(String vowelStr, char c) {return vowelStr.indexOf(c) >= 0;}}