比如我创建一个Kotlin Object类：ObjectMethod
package com.baichuan.example.unit_test
object ObjectMethod {
fun doSomething() {
println("this is ObjectMethod#doSomething")
}
@JvmStatic
fun 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`<Unit>(
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 {
@NotNull
public 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);
}
@JvmStatic
public 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_test
import java.lang.reflect.Field
import java.lang.reflect.Modifier
object ReflectionUtils {
@Throws(Exception::class)
fun setFinalStatic(field: Field, newValue: Any) {
field.isAccessible = true
val modifiersField: Field = Field::class.java.getDeclaredField("modifiers")
modifiersField.isAccessible = true
modifiersField.setInt(field, field.modifiers and Modifier.FINAL.inv())
field.set(null, newValue)
}
}
github
https://github.com/scientificCommunity/blog-sample/tree/main/unit-test-sample
