Mockito|Mockito mock Kotlin Object类方法报错解决方法 MockitomockKotlinObject类方法报错解

比如我创建一个Kotlin Object类：ObjectMethod

package com.baichuan.example.unit_testobject ObjectMethod {fun doSomething() {println("this is ObjectMethod#doSomething")}@JvmStaticfun doSomethingWithJvmStatic() {println("this is ObjectMethod#doSomethingWithJvmStatic")}}

如果我直接去mock该类的doSomething方法，会报错。

@Test@DisplayName("mock普通的kotlin静态方法")fun testMockKotlinObject() {Assertions.assertThrows(MissingMethodInvocationException::class.java) {Mockito.mockStatic(ObjectMethod::class.java).`when`(ObjectMethod::doSomething).thenAnswer { println("this is mocked Object#doSomething") }}ObjectMethod.doSomething()}

这是因为kotlin里的object类里的方法虽然在kotlin里从形态跟使用上来看与静态方法无二。但是编译成java代码后，其本质其实是内部初始化了一个当前类的静态常量实例INSTANCE。这个INSTANCE在kotlin语法里被隐藏了，但在java里依然可以显示访问。ObjectMethod编译成java后的代码如下：

public final class ObjectMethod {@NotNullpublic static final ObjectMethod INSTANCE = new ObjectMethod(); private ObjectMethod() {}public final void doSomething() {String var1 = "this is ObjectMethod#doSomething"; boolean var2 = false; System.out.println(var1); }@JvmStaticpublic static final void doSomethingWithJvmStatic() {String var0 = "this is ObjectMethod#doSomethingWithJvmStatic"; boolean var1 = false; System.out.println(var0); }}

所以，不能mock ObjectMethod#doSomething本质上的原因是正常手段无法mock静态常量。如果想要使kotlin的object类中的方法能够被mock，只需在方法上加上@JvmStatic注解即可。被其标注的方法会被编译成普通的java静态方法。
上面说正常手段无法mock静态常量，那么非正常手段呢？其实这个非正常手段就是通过反射将被mock过的实例注入到ObjectMethod中即可。

@Test @DisplayName("通过反射修改静态常量来mock普通的kotlin静态方法") fun testMockKotlinObjectMethodByReflection() {val mock = Mockito.mock(ObjectMethod::class.java)Mockito.`when`(mock.doSomething()).then {print("this is mocked ObjectMethod by reflection")}val declaredMethod = ObjectMethod::class.java.getDeclaredField("INSTANCE")ReflectionUtils.setFinalStatic(declaredMethod, mock) ObjectMethod.doSomething() }

ReflectionUtils

package com.baichuan.example.unit_testimport java.lang.reflect.Fieldimport java.lang.reflect.Modifierobject ReflectionUtils {@Throws(Exception::class)fun setFinalStatic(field: Field, newValue: Any) {field.isAccessible = trueval modifiersField: Field = Field::class.java.getDeclaredField("modifiers")modifiersField.isAccessible = truemodifiersField.setInt(field, field.modifiers and Modifier.FINAL.inv())field.set(null, newValue)}}

github
https://github.com/scientificCommunity/blog-sample/tree/main/unit-test-sample
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