编写干净的测试–分而治之

好的单元测试应该仅出于一个原因而失败。这意味着适当的单元测试仅测试一个逻辑概念。

如果我们要编写干净的测试，则必须识别这些逻辑概念，并且每个逻辑概念仅编写一个测试用例。

这篇博客文章描述了我们如何识别从测试中发现的逻辑概念，以及如何将现有的单元测试分成多个单元测试。

干净还不够好

让我们先看一下单元测试的源代码，该源代码确保当使用唯一的电子邮件地址和社交登录提供者创建新用户帐户时， RepositoryUserService类的registerNewUserAccount（RegistrationForm userAccountData）方法能够按预期工作。

该单元测试的源代码如下所示：

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mock;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.runners.MockitoJUnitRunner;
import org.mockito.stubbing.Answer;
import org.springframework.security.crypto.password.PasswordEncoder;import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertNull;
import static org.mockito.Matchers.isA;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyNoMoreInteractions;
import static org.mockito.Mockito.verifyZeroInteractions;
import static org.mockito.Mockito.when;@RunWith(MockitoJUnitRunner.class)
public class RepositoryUserServiceTest {private static final String REGISTRATION_EMAIL_ADDRESS = "john.smith@gmail.com";private static final String REGISTRATION_FIRST_NAME = "John";private static final String REGISTRATION_LAST_NAME = "Smith";private static final SocialMediaService SOCIAL_SIGN_IN_PROVIDER = SocialMediaService.TWITTER;private RepositoryUserService registrationService;@Mockprivate PasswordEncoder passwordEncoder;@Mockprivate UserRepository repository;@Beforepublic void setUp() {registrationService = new RepositoryUserService(passwordEncoder, repository);}@Testpublic void registerNewUserAccount_SocialSignInAndUniqueEmail_ShouldCreateNewUserAccountAndSetSignInProvider() throws DuplicateEmailException {RegistrationForm registration = new RegistrationFormBuilder().email(REGISTRATION_EMAIL_ADDRESS).firstName(REGISTRATION_FIRST_NAME).lastName(REGISTRATION_LAST_NAME).isSocialSignInViaSignInProvider(SOCIAL_SIGN_IN_PROVIDER).build();when(repository.findByEmail(REGISTRATION_EMAIL_ADDRESS)).thenReturn(null);when(repository.save(isA(User.class))).thenAnswer(new Answer<User>() {@Overridepublic User answer(InvocationOnMock invocation) throws Throwable {Object[] arguments = invocation.getArguments();return (User) arguments[0];}});User createdUserAccount = registrationService.registerNewUserAccount(registration);assertThat(createdUserAccount).hasEmail(REGISTRATION_EMAIL_ADDRESS).hasFirstName(REGISTRATION_FIRST_NAME).hasLastName(REGISTRATION_LAST_NAME).isRegisteredUser().isRegisteredByUsingSignInProvider(SOCIAL_SIGN_IN_PROVIDER);verify(repository, times(1)).findByEmail(REGISTRATION_EMAIL_ADDRESS);verify(repository, times(1)).save(createdUserAccount);verifyNoMoreInteractions(repository);verifyZeroInteractions(passwordEncoder);}
}

这个单元测试非常干净。毕竟，我们的测试类，测试方法以及在测试方法内部创建的局部变量具有描述性名称。我们还用常数替换了幻数，并创建了特定领域的语言来创建新对象和编写断言。

但是， 我们可以使这项测试更好 。

这个单元测试的问题是它可能由于多种原因而失败。如果发生以下情况，它将失败：

我们的服务方法不会检查是否从我们的数据库中找不到输入到注册表中的电子邮件地址。
持久化的User对象的信息与在注册表中输入的信息不匹配。
返回的User对象的信息不正确。
我们的服务方法通过使用PasswordEncoder对象为用户创建密码。

换句话说，此单元测试测试了四个不同的逻辑概念，这导致以下问题：

如果此测试失败，我们不一定知道为什么失败。这意味着我们必须阅读单元测试的源代码。
单元测试有点长，这使得阅读起来有些困难。
很难描述预期的行为。这意味着很难为我们的测试方法找到好名字。

通过确定该单元测试将失败的情况，我们可以确定单个单元测试所涵盖的逻辑概念。

这就是为什么我们需要将此测试分为四个单元测试。

一测试，一故障

下一步是将单元测试分成四个新的单元测试，并确保每个单元测试都测试一个逻辑概念。我们可以通过编写以下单元测试来做到这一点：

我们需要确保我们的服务方法检查用户提供的电子邮件地址是否唯一。
我们需要验证持久性User对象的信息是否正确。
我们需要确保返回的User对象的信息正确。
我们需要验证我们的服务方法没有为使用社交登录提供商的用户创建编码密码。

编写完这些单元测试之后，测试类的源代码如下所示：

import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.ArgumentCaptor;
import org.mockito.Mock;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.runners.MockitoJUnitRunner;
import org.mockito.stubbing.Answer;
import org.springframework.security.crypto.password.PasswordEncoder;import static net.petrikainulainen.spring.social.signinmvc.user.model.UserAssert.assertThat;
import static org.mockito.Matchers.isA;
import static org.mockito.Mockito.times;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.verifyZeroInteractions;
import static org.mockito.Mockito.when;@RunWith(MockitoJUnitRunner.class)
public class RepositoryUserServiceTest {private static final String REGISTRATION_EMAIL_ADDRESS = "john.smith@gmail.com";private static final String REGISTRATION_FIRST_NAME = "John";private static final String REGISTRATION_LAST_NAME = "Smith";private static final SocialMediaService SOCIAL_SIGN_IN_PROVIDER = SocialMediaService.TWITTER;private RepositoryUserService registrationService;@Mockprivate PasswordEncoder passwordEncoder;@Mockprivate UserRepository repository;@Beforepublic void setUp() {registrationService = new RepositoryUserService(passwordEncoder, repository);}@Testpublic void registerNewUserAccount_SocialSignInAndUniqueEmail_ShouldCheckThatEmailIsUnique() throws DuplicateEmailException {RegistrationForm registration = new RegistrationFormBuilder().email(REGISTRATION_EMAIL_ADDRESS).firstName(REGISTRATION_FIRST_NAME).lastName(REGISTRATION_LAST_NAME).isSocialSignInViaSignInProvider(SOCIAL_SIGN_IN_PROVIDER).build();when(repository.findByEmail(REGISTRATION_EMAIL_ADDRESS)).thenReturn(null);registrationService.registerNewUserAccount(registration);verify(repository, times(1)).findByEmail(REGISTRATION_EMAIL_ADDRESS);}@Testpublic void registerNewUserAccount_SocialSignInAndUniqueEmail_ShouldSaveNewUserAccountAndSetSignInProvider() throws DuplicateEmailException {RegistrationForm registration = new RegistrationFormBuilder().email(REGISTRATION_EMAIL_ADDRESS).firstName(REGISTRATION_FIRST_NAME).lastName(REGISTRATION_LAST_NAME).isSocialSignInViaSignInProvider(SOCIAL_SIGN_IN_PROVIDER).build();when(repository.findByEmail(REGISTRATION_EMAIL_ADDRESS)).thenReturn(null);registrationService.registerNewUserAccount(registration);ArgumentCaptor<User> userAccountArgument = ArgumentCaptor.forClass(User.class);verify(repository, times(1)).save(userAccountArgument.capture());User createdUserAccount = userAccountArgument.getValue();assertThat(createdUserAccount).hasEmail(REGISTRATION_EMAIL_ADDRESS).hasFirstName(REGISTRATION_FIRST_NAME).hasLastName(REGISTRATION_LAST_NAME).isRegisteredUser().isRegisteredByUsingSignInProvider(SOCIAL_SIGN_IN_PROVIDER);}@Testpublic void registerNewUserAccount_SocialSignInAndUniqueEmail_ShouldReturnCreatedUserAccount() throws DuplicateEmailException {RegistrationForm registration = new RegistrationFormBuilder().email(REGISTRATION_EMAIL_ADDRESS).firstName(REGISTRATION_FIRST_NAME).lastName(REGISTRATION_LAST_NAME).isSocialSignInViaSignInProvider(SOCIAL_SIGN_IN_PROVIDER).build();when(repository.findByEmail(REGISTRATION_EMAIL_ADDRESS)).thenReturn(null);when(repository.save(isA(User.class))).thenAnswer(new Answer<User>() {@Overridepublic User answer(InvocationOnMock invocation) throws Throwable {Object[] arguments = invocation.getArguments();return (User) arguments[0];}});User createdUserAccount = registrationService.registerNewUserAccount(registration);assertThat(createdUserAccount).hasEmail(REGISTRATION_EMAIL_ADDRESS).hasFirstName(REGISTRATION_FIRST_NAME).hasLastName(REGISTRATION_LAST_NAME).isRegisteredUser().isRegisteredByUsingSignInProvider(SOCIAL_SIGN_IN_PROVIDER);}@Testpublic void registerNewUserAccount_SocialSignInAnUniqueEmail_ShouldNotCreateEncodedPasswordForUser() throws DuplicateEmailException {RegistrationForm registration = new RegistrationFormBuilder().email(REGISTRATION_EMAIL_ADDRESS).firstName(REGISTRATION_FIRST_NAME).lastName(REGISTRATION_LAST_NAME).isSocialSignInViaSignInProvider(SOCIAL_SIGN_IN_PROVIDER).build();when(repository.findByEmail(REGISTRATION_EMAIL_ADDRESS)).thenReturn(null);registrationService.registerNewUserAccount(registration);verifyZeroInteractions(passwordEncoder);}
}

编写仅测试一个逻辑概念的单元测试的明显好处是，很容易知道为什么测试失败。但是，此方法还有其他两个好处：