在JUnit测试中使用Builder模式

这并不是要成为技术含量很高的职位。这篇文章的目的是为您提供一些指导，以使您的JUnit测试生活更加轻松，使您能够在几分钟内编写复杂的测试场景，并具有易于阅读的测试优势。

单元测试中有两个主要部分，需要编写许多引导程序代码：

设置部分：构建初始状态需要构建将被馈送到SUT（被测系统）的初始对象
断言部分：构造输出对象的所需图像，并仅对所需数据进行断言。

为了降低构建用于测试的对象的复杂性，我建议在以下解释中使用Builder模式：

这是域对象：

public class Employee {private int id;private String name;private Department department;//setters, getters, hashCode, equals, toString methods

此域对象的生成器如下所示：

public class EmployeeBuilder {private Employee employee;public EmployeeBuilder() {employee = new Employee();}public static EmployeeBuilder defaultValues() {return new EmployeeBuilder();}public static EmployeeBuilder clone(Employee toClone) {EmployeeBuilder builder = defaultValues();builder.setId(toClone.getId());builder.setName(toClone.getName());builder.setDepartment(toClone.getDepartment());return builder;}public static EmployeeBuilder random() {EmployeeBuilder builder = defaultValues();builder.setId(getRandomInteger(0, 1000));builder.setName(getRandomString(20));builder.setDepartment(Department.values()[getRandomInteger(0, Department.values().length - 1)]);return builder;}public EmployeeBuilder setId(int id) {employee.setId(id);return this;}public EmployeeBuilder setName(String name) {employee.setName(name);return this;}public EmployeeBuilder setDepartment(Department dept) {employee.setDepartment(dept);return this;}public Employee build() {return employee;}
}

如您所见，我们有一些工厂方法：

public static EmployeeBuilder defaultValues()public static EmployeeBuilder clone(Employee toClone)public static EmployeeBuilder random()

这些方法返回不同的构建器：

defaultValues：每个字段的一些硬编码值（或Java默认值-当前实现）
clone：将获取初始对象中的所有值，并使您可以更改其中一些值
random：将为每个字段生成随机值。当您有很多字段在测试中不需要时非常有用，但是您需要将它们初始化。 getRandom *方法是在另一个类中静态定义的。

您可以添加其他方法来根据需要初始化构建器。

此外，构建器还可以处理一些不那么容易构建和更改的对象。例如，让我们稍微更改Employee对象，使其不可变：

public class Employee {private final int id;private final String name;private final Department department;...
}

现在，我们失去了按需更改字段的可能性。但是使用以下形式的构建器，我们可以在构造对象时重新获得这种可能性：

public class ImmutableEmployeeBuilder {private int id;private String name;private Department department;public ImmutableEmployeeBuilder() {}public static ImmutableEmployeeBuilder defaultValues() {return new ImmutableEmployeeBuilder();}public static ImmutableEmployeeBuilder clone(Employee toClone) {ImmutableEmployeeBuilder builder = defaultValues();builder.setId(toClone.getId());builder.setName(toClone.getName());builder.setDepartment(toClone.getDepartment());return builder;}public static ImmutableEmployeeBuilder random() {ImmutableEmployeeBuilder builder = defaultValues();builder.setId(getRandomInteger(0, 1000));builder.setName(getRandomString(20));builder.setDepartment(Department.values()[getRandomInteger(0, Department.values().length - 1)]);return builder;}public ImmutableEmployeeBuilder setId(int id) {this.id = id;return this;}public ImmutableEmployeeBuilder setName(String name) {this.name = name;return this;}public ImmutableEmployeeBuilder setDepartment(Department dept) {this.department = dept;return this;}public ImmutableEmployee build() {return new ImmutableEmployee(id, name, department);}
}

当我们难以构造对象或需要更改最终字段时，这非常有用。

这是它的最终结果：

没有建设者：

@Testpublic void changeRoleTestWithoutBuilders() {// building the initial stateEmployee employee = new Employee();employee.setId(1);employee.setDepartment(Department.DEVELOPEMENT);employee.setName("John Johnny");// testing the SUTEmployeeManager employeeManager = new EmployeeManager();employeeManager.changeRole(employee, Department.MANAGEMENT);// building the expectationsEmployee expectedEmployee = new Employee();expectedEmployee.setId(employee.getId());expectedEmployee.setDepartment(Department.MANAGEMENT);expectedEmployee.setName(employee.getName());// assertionsassertThat(employee, is(expectedEmployee));}

与建设者：

@Testpublic void changeRoleTestWithBuilders() {// building the initial stateEmployee employee = EmployeeBuilder.defaultValues().setId(1).setName("John Johnny").setDepartment(Department.DEVELOPEMENT).build();// building the expectationsEmployee expectedEmployee = EmployeeBuilder.clone(employee).setDepartment(Department.MANAGEMENT).build();// testing the SUTEmployeeManager employeeManager = new EmployeeManager();employeeManager.changeRole(employee, Department.MANAGEMENT);// assertionsassertThat(employee, is(expectedEmployee));}

如您所见，测试的大小要小得多，对象的构造也变得更加简单（如果代码格式更好，也会更好）。如果您具有更复杂的域对象（在实际应用程序中，尤其是在遗留代码中），则差异更大。

玩得开心！

参考：来自Java出现日历博客的JCG合作伙伴 Stefan Bulzan 在JUnit测试中使用了Builder模式。