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Mockito how to mock a private method [duplicate]

public class A {
public void method(boolean b){
if (b == true)
method1();
else
method2();
}
private void method1() {}
private void method2() {}
}
public class TestA {
#Test
public void testMethod() {
A a = mock(A.class);
a.method(true);
//how to test like verify(a).method1();
}
}
How to test private method is called or not, and how to test private method using mockito?

Not possible through mockito. From their wiki
Why Mockito doesn't mock private methods?
Firstly, we are not dogmatic about mocking private methods. We just
don't care about private methods because from the standpoint of
testing private methods don't exist. Here are a couple of reasons
Mockito doesn't mock private methods:
It requires hacking of classloaders that is never bullet proof and it
changes the api (you must use custom test runner, annotate the class,
etc.).
It is very easy to work around - just change the visibility of method
from private to package-protected (or protected).
It requires me to spend time implementing & maintaining it. And it
does not make sense given point #2 and a fact that it is already
implemented in different tool (powermock).
Finally... Mocking private methods is a hint that there is something
wrong with OO understanding. In OO you want objects (or roles) to
collaborate, not methods. Forget about pascal & procedural code. Think
in objects.

You can't do that with Mockito but you can use Powermock to extend Mockito and mock private methods. Powermock supports Mockito. Here's an example.

Here is a small example how to do it with powermock
public class Hello {
private Hello obj;
private Integer method1(Long id) {
return id + 10;
}
}
To test method1 use code:
Hello testObj = new Hello();
Integer result = Whitebox.invokeMethod(testObj, "method1", new Long(10L));
To set private object obj use this:
Hello testObj = new Hello();
Hello newObject = new Hello();
Whitebox.setInternalState(testObj, "obj", newObject);

While Mockito doesn't provide that capability, you can achieve the same result using Mockito + the JUnit ReflectionUtils class or the Spring ReflectionTestUtils class. Please see an example below taken from here explaining how to invoke a private method:
ReflectionTestUtils.invokeMethod(student, "saveOrUpdate", "From Unit test");
Complete examples with ReflectionTestUtils and Mockito can be found in the book Mockito for Spring.
Official documentation Spring Testing

By using reflection, private methods can be called from test classes.
In this case,
//test method will be like this ...
public class TestA {
#Test
public void testMethod() {
A a= new A();
Method privateMethod = A.class.getDeclaredMethod("method1", null);
privateMethod.setAccessible(true);
// invoke the private method for test
privateMethod.invoke(A, null);
}
}
If the private method calls any other private method, then we need to spy the object and stub the another method.The test class will be like ...
//test method will be like this ...
public class TestA {
#Test
public void testMethod() {
A a= new A();
A spyA = spy(a);
Method privateMethod = A.class.getDeclaredMethod("method1", null);
privateMethod.setAccessible(true);
doReturn("Test").when(spyA, "method2"); // if private method2 is returning string data
// invoke the private method for test
privateMethod.invoke(spyA , null);
}
}
**The approach is to combine reflection and spying the object.
**method1 and **method2 are private methods and method1 calls method2.

Think about this in terms of behaviour, not in terms of what methods there are. The method called method has a particular behaviour if b is true. It has different behaviour if b is false. This means you should write two different tests for method; one for each case. So instead of having three method-oriented tests (one for method, one for method1, one for method2, you have two behaviour-oriented tests.
Related to this (I suggested this in another SO thread recently, and got called a four-letter word as a result, so feel free to take this with a grain of salt); I find it helpful to choose test names that reflect the behaviour that I'm testing, rather than the name of the method. So don't call your tests testMethod(), testMethod1(), testMethod2() and so forth. I like names like calculatedPriceIsBasePricePlusTax() or taxIsExcludedWhenExcludeIsTrue() that indicate what behaviour I'm testing; then within each test method, test only the indicated behaviour. Most such behaviours will involve just one call to a public method, but may involve many calls to private methods.
Hope this helps.

I was able to test a private method inside using mockito using reflection.
Here is the example, tried to name it such that it makes sense
//Service containing the mock method is injected with mockObjects
#InjectMocks
private ServiceContainingPrivateMethod serviceContainingPrivateMethod;
//Using reflection to change accessibility of the private method
Class<?>[] params = new Class<?>[]{PrivateMethodParameterOne.class, PrivateMethodParameterTwo.class};
Method m = serviceContainingPrivateMethod .getClass().getDeclaredMethod("privateMethod", params);
//making private method accessible
m.setAccessible(true);
assertNotNull(m.invoke(serviceContainingPrivateMethod, privateMethodParameterOne, privateMethodParameterTwo).equals(null));

You're not suppose to test private methods. Only non-private methods needs to be tested as these should call the private methods anyway. If you "want" to test private methods, it may indicate that you need to rethink your design:
Am I using proper dependency injection?
Do I possibly needs to move the private methods into a separate class and rather test that?
Must these methods be private? ...can't they be default or protected rather?
In the above instance, the two methods that are called "randomly" may actually need to be placed in a class of their own, tested and then injected into the class above.

There is actually a way to test methods from a private member with Mockito. Let's say you have a class like this:
public class A {
private SomeOtherClass someOtherClass;
A() {
someOtherClass = new SomeOtherClass();
}
public void method(boolean b){
if (b == true)
someOtherClass.method1();
else
someOtherClass.method2();
}
}
public class SomeOtherClass {
public void method1() {}
public void method2() {}
}
If you want to test a.method will invoke a method from SomeOtherClass, you can write something like below.
#Test
public void testPrivateMemberMethodCalled() {
A a = new A();
SomeOtherClass someOtherClass = Mockito.spy(new SomeOtherClass());
ReflectionTestUtils.setField( a, "someOtherClass", someOtherClass);
a.method( true );
Mockito.verify( someOtherClass, Mockito.times( 1 ) ).method1();
}
ReflectionTestUtils.setField(); will stub the private member with something you can spy on.

I don't really understand your need to test the private method. The root problem is that your public method has void as return type, and hence you are not able to test your public method. Hence you are forced to test your private method. Is my guess correct??
A few possible solutions (AFAIK):
Mocking your private methods, but still you won't be "actually" testing your methods.
Verify the state of object used in the method. MOSTLY methods either do some processing of the input values and return an output, or change the state of the objects. Testing the objects for the desired state can also be employed.
public class A{
SomeClass classObj = null;
public void publicMethod(){
privateMethod();
}
private void privateMethod(){
classObj = new SomeClass();
}
}
[Here you can test for the private method, by checking the state change of the classObj from null to not null.]
Refactor your code a little (Hope this is not a legacy code). My funda of writing a method is that, one should always return something (a int/ a boolean). The returned value MAY or MAY NOT be used by the implementation, but it will SURELY BE used by the test
code.
public class A
{
public int method(boolean b)
{
int nReturn = 0;
if (b == true)
nReturn = method1();
else
nReturn = method2();
}
private int method1() {}
private int method2() {}
}

Put your test in the same package, but a different source folder (src/main/java vs. src/test/java) and make those methods package-private. Imo testability is more important than privacy.

In cases where the private method is not void and the return value is used as a parameter to an external dependency's method, you can mock the dependency and use an ArgumentCaptor to capture the return value.
For example:
ArgumentCaptor<ByteArrayOutputStream> csvOutputCaptor = ArgumentCaptor.forClass(ByteArrayOutputStream.class);
//Do your thing..
verify(this.awsService).uploadFile(csvOutputCaptor.capture());
....
assertEquals(csvOutputCaptor.getValue().toString(), "blabla");

Building on #aravind-yarram's answer: Not possible through mockito. From their wiki
So what's the OO way of testing private methods? Private methods with complex logic might be a sign that your class is violating the principle of single responsibility and that some of the logic should be moved to a new class.
Indeed, by extracting those private methods to public methods of more granular classes, you can unit test them without breaking the encapsulation of your original class.

Access private method of an instance in unit test

I came across the following issue when I was trying to unit test my code. If I have a class that creates an instance and for example a getter method like this:
public class Test {
private static Test instance;
private ArrayList<String> arrayList = new ArrayList<String>();
public static Test getInstance() {
return instance;
}
private ArrayList<String> getArrayList() {
return arrayList;
}
}
If now I want to access the arrayList in a test case it would fail, because the list is returned by a non-accessable private method. So trying something like this wouldn't work:
public class AccessTest {
private Test test;
public void accessList(){
test = Test.getInstance();
test.getArrayList();
}
}
So one way to access the arrayList anyway, would probably be to change the visibility to protected. But isn't there a better way to access the method? Is it really necessary to make a method protected only because of a test that needs to access it?

In general, if you have some private methods in your class and you feel that you have problems with testing them, it is a sign of a bit of a code smell. It shows that too many functionality is hidden behind private wall.
You could change visibility of such method to package protected, so JUnit test will see it. There is also a Google Guava annotation #VisibleForTesting or something like that. But again - this is a sign of wrong class design.
Think of extracting such method to a separate class and make that methods public then.
For example, take a look at the following code:
class ReportCreator {
public File createSomeImportantReport(LocalDate date) {
String fileName = provideFileName(date);
File result = new File(fileName);
return result;
}
private String provideFileName(LocalDate date) {
// ... some complex business logic to generate file name based on date... ;)
return fileName;
}
}
There is a private method provideFileName() that does some complicated things and let's say it's hard to test if you would test only createSomeImportantReport().
See what changes if you externalize that functionality.
class ReportCreator {
private FileNameProvider fileNameProvider;
public File createSomeImportantReport(LocalDate date) {
File result = new File(fileNameProvider.provideFileName(date));
return result;
}
}
class FileNameProvider {
public String provideFileName(LocalDate date) {
return ......;
}
}
You now have option to test that thing separately, focus on what's important in that particular case.

Despite the fact that I don't see a use case for a private getter, you can use the package private access level. This is the default access level so you don't have to specify it. You can then test it by adding the test class in the same package name in the test directory. For instance the class is located in src/main/java/application and the test class can then be located in src/test/java/application.

Use Java Reflection for that:
Test test = new Test();
Method getArrayListMethod = test.getClass().getDeclaredMethod("getArrayList", null);
getArrayListMethod.setAccessible(true);
ArrayList<String> list = (ArrayList<String>) getArrayListMethod .invoke(test);
System.out.println(list); // Prints the list
Create your Test object, use the method getClass() and get the method declared on that class by its name.
Then set that method accessible dynamically. If you know the data type that it returns, then cast it to it.

Test tightly coupled classes in Java

I have this original code:
public SomeClass(int parameter) {
this.someProperty = parameter;
this.apiObject = new SomeApiClass(someProperty);
for(i=0; i < 2; i++)
apiObject.setApiProperty(i, "Hello World");
}
The code works perfectly fine. But the problem arises when I try to test the same.
#Mock
private SomeApiClass someApiClass;
private SomeClass someClass;
#Before
public void setUp() throws Exception {
someClass = new SomeClass(3);
}
#Test
public void shouldCreateSomeClass() {
verify(someApiClass, times(2)). setApiProperty(anyInt(),anyString());
}
I understand why this test wouldn't pass. This would work if I change the constructor to this:
public SomeClass(int parameter, SomeApiClass someApiClass) {
...
}
How do I test the original code if I do not want to inject SomeApiClass to the constructor and also can't afford to provide any getters in it.
PS: Please ignore typos in the code. Typed it on the fly.

It's good to think about testability when you design your class and also to differentiate parameters and dependencies.
Dependencies are objects that the class will rely on to get its work done. They generally don't change throughout the lifecycle of the dependee object.
Parameters are more localized than dependencies. They are expected to change in between calls to the methods of the object.
In the original code, it looks like the work done in the constructor for SomeClass should really go inside a method:
public class SomeClass {
public void doWork(int parameter) {
//
}
}
Inside the method, if you are only interested in instantiating SomeApiObject with the parameter, then why not follow the Law of Demeter and pass in directly SomeApiObject as a parameter:
public void doWork(SomeApiObject someApiObject) {
//
}
Then the consumer does the work:
someClass.doWork(new SomeApiObject(3));
and it can be tested by passing in a mocked SomeApiObject as a parameter:
//act
someClass.doWork(mockedSomeApiObject);
//assert
verify(mockedSomeApiObject).someVerification();
However, if you want a combination of parameters and dependencies you can use a Factory as a dependency:
public class SomeClass {
private final SomeApiObjectFactory someApiObjectFactory;
public SomeClass(SomeApiObjectFactory someApiObjectFactory) {
this.someApiObjectFactory = someApiObjectFactory;
}
public void doWork(int parameter) {
SomeApiObject someApiObject = someApiObjectFactory.create(parameter);
//etc
}
Then you can now test the class since you have a way to supply mocks on which behaviour can be verified:
SomeApiObject mockSomeApiObject = Mockito.mock(SomeApiObject.class);
when(mockSomeApiObjectFactory.create(anyInt()).thenReturn(mockApiObject);
Aside from all of that there are ways of using Powermockito to test your original class as it is without alteration but these are not ideal and it is best to refactor if possible so you can use plain Mockito to test. This will give you good OO habits. Good luck!

Running JUnit tests with different data

I have a suite of unit tests. I have a static variable which gets initialized in setup() method. I want to run all my suite of unit tests with two different values of that static variable.
Static variable in setup() gets initialized to an object which is a singleton. So, I can't(I think I can't) use JUnit parametrized tests.
I have to run all the tests with one value of that static variable, and then run all the tests with other value of static variable.
Any ideas on how to do this in an elegant way if possible.
Code below if my description above is not very easy to understand
public class MyClassTest{
private static final Dep_class dep_obj;
public static void setup(){
dep_obj = Dep_class.getInstance("VALUE_1");
//You can have only instance of Dep_class at any time.
//So for second run I need to do a
//dep_obj = Dep_class.getInstance("VALUE_2") and run my tests.
}
public void test_mymethod(){
//do something with dep_obj
}

Try this
#RunWith(Parameterized.class)
public class MyClassTest {
private Object dep_obj;
public MyClassTest(String val) {
dep_obj = val;
}
#Parameters
public static Collection<?> data() {
Object[][] data = { { "val1" }, { "val2" }, { "val3" } };
return Arrays.asList(data);
}
#Test
public void test() {
System.out.println(dep_obj);
}
}

So first of all, I would question why you have a singleton that is initialized in this way. It seems as if adding an argument to your .getInstance(String s) method would add ambiguity and unexpected behavior, as this String argument will just be disregarded after instantiation (unless you're re-instantiating it if the type changes, in which case it will be highly unpredictable at runtime).
In any case, an easy way to do this would be to abstract the test_mymethod() to a parent class and have two child test classes that each instantiate a different instance of the singleton. Since your JVM will not restart, you'll also need something like PowerMock to reset the singleton to a pre-loaded state before running any tests.
So the parent class would look like so (JUnit annotations added):
public abstract class MyAbstractTestClass {
private final Dep_class dep_obj;
#Before
public abstract void setup(){
// Begin by ensuring that the singleton instance is initialized to null -
// this is highly important, since subclasses will not be able to rely on
// an un-initialized state
Whitebox.setInternalState(dep_obj.getInstance(/*default, arbitrary, or null value*/, "instance", null);
// Now leave the actual singleton initialization to child classes
dep_obj = getSingleton();
}
public abstract Dep_class getSingleton();
#Test
public void test_mymethod(){
//do something with dep_obj
}
}
I made a few assumptions with Powermock - namely that your singleton properly checks to see if the instance is null and if so, initializes it. In this case, I'm assuming that the variable name for your instance is "instance". Next, your child classes would look like this:
public class MyTestClass1 extends MyAbstractTestClass {
#Override
public void Dep_class getSingleton() {
return Dep_class.getInstance("VALUE_1");
}
}
public class MyTestClass2 extends MyAbstractTestClass {
#Override
public void Dep_class getSingleton() {
return Dep_class.getInstance("VALUE_2");
}
}
Again, I would strongly encourage you to re-think implementing a singleton in this way. Singletons should be rarely used anyway - an implementation like this on top of a questionable design pattern is an eyebrow raiser. This question goes over some good guidelines for usage - make sure that your singleton fits this criteria.

Testing Private method using mockito

public class A {
public void method(boolean b){
if (b == true)
method1();
else
method2();
}
private void method1() {}
private void method2() {}
}
public class TestA {
#Test
public void testMethod() {
A a = mock(A.class);
a.method(true);
//how to test like verify(a).method1();
}
}
How to test private method is called or not, and how to test private method using mockito?

Not possible through mockito. From their wiki
Why Mockito doesn't mock private methods?
Firstly, we are not dogmatic about mocking private methods. We just
don't care about private methods because from the standpoint of
testing private methods don't exist. Here are a couple of reasons
Mockito doesn't mock private methods:
It requires hacking of classloaders that is never bullet proof and it
changes the api (you must use custom test runner, annotate the class,
etc.).
It is very easy to work around - just change the visibility of method
from private to package-protected (or protected).
It requires me to spend time implementing & maintaining it. And it
does not make sense given point #2 and a fact that it is already
implemented in different tool (powermock).
Finally... Mocking private methods is a hint that there is something
wrong with OO understanding. In OO you want objects (or roles) to
collaborate, not methods. Forget about pascal & procedural code. Think
in objects.

You can't do that with Mockito but you can use Powermock to extend Mockito and mock private methods. Powermock supports Mockito. Here's an example.

Here is a small example how to do it with powermock
public class Hello {
private Hello obj;
private Integer method1(Long id) {
return id + 10;
}
}
To test method1 use code:
Hello testObj = new Hello();
Integer result = Whitebox.invokeMethod(testObj, "method1", new Long(10L));
To set private object obj use this:
Hello testObj = new Hello();
Hello newObject = new Hello();
Whitebox.setInternalState(testObj, "obj", newObject);

While Mockito doesn't provide that capability, you can achieve the same result using Mockito + the JUnit ReflectionUtils class or the Spring ReflectionTestUtils class. Please see an example below taken from here explaining how to invoke a private method:
ReflectionTestUtils.invokeMethod(student, "saveOrUpdate", "From Unit test");
Complete examples with ReflectionTestUtils and Mockito can be found in the book Mockito for Spring.
Official documentation Spring Testing

By using reflection, private methods can be called from test classes.
In this case,
//test method will be like this ...
public class TestA {
#Test
public void testMethod() {
A a= new A();
Method privateMethod = A.class.getDeclaredMethod("method1", null);
privateMethod.setAccessible(true);
// invoke the private method for test
privateMethod.invoke(A, null);
}
}
If the private method calls any other private method, then we need to spy the object and stub the another method.The test class will be like ...
//test method will be like this ...
public class TestA {
#Test
public void testMethod() {
A a= new A();
A spyA = spy(a);
Method privateMethod = A.class.getDeclaredMethod("method1", null);
privateMethod.setAccessible(true);
doReturn("Test").when(spyA, "method2"); // if private method2 is returning string data
// invoke the private method for test
privateMethod.invoke(spyA , null);
}
}
**The approach is to combine reflection and spying the object.
**method1 and **method2 are private methods and method1 calls method2.

Think about this in terms of behaviour, not in terms of what methods there are. The method called method has a particular behaviour if b is true. It has different behaviour if b is false. This means you should write two different tests for method; one for each case. So instead of having three method-oriented tests (one for method, one for method1, one for method2, you have two behaviour-oriented tests.
Related to this (I suggested this in another SO thread recently, and got called a four-letter word as a result, so feel free to take this with a grain of salt); I find it helpful to choose test names that reflect the behaviour that I'm testing, rather than the name of the method. So don't call your tests testMethod(), testMethod1(), testMethod2() and so forth. I like names like calculatedPriceIsBasePricePlusTax() or taxIsExcludedWhenExcludeIsTrue() that indicate what behaviour I'm testing; then within each test method, test only the indicated behaviour. Most such behaviours will involve just one call to a public method, but may involve many calls to private methods.
Hope this helps.

I was able to test a private method inside using mockito using reflection.
Here is the example, tried to name it such that it makes sense
//Service containing the mock method is injected with mockObjects
#InjectMocks
private ServiceContainingPrivateMethod serviceContainingPrivateMethod;
//Using reflection to change accessibility of the private method
Class<?>[] params = new Class<?>[]{PrivateMethodParameterOne.class, PrivateMethodParameterTwo.class};
Method m = serviceContainingPrivateMethod .getClass().getDeclaredMethod("privateMethod", params);
//making private method accessible
m.setAccessible(true);
assertNotNull(m.invoke(serviceContainingPrivateMethod, privateMethodParameterOne, privateMethodParameterTwo).equals(null));

You're not suppose to test private methods. Only non-private methods needs to be tested as these should call the private methods anyway. If you "want" to test private methods, it may indicate that you need to rethink your design:
Am I using proper dependency injection?
Do I possibly needs to move the private methods into a separate class and rather test that?
Must these methods be private? ...can't they be default or protected rather?
In the above instance, the two methods that are called "randomly" may actually need to be placed in a class of their own, tested and then injected into the class above.

There is actually a way to test methods from a private member with Mockito. Let's say you have a class like this:
public class A {
private SomeOtherClass someOtherClass;
A() {
someOtherClass = new SomeOtherClass();
}
public void method(boolean b){
if (b == true)
someOtherClass.method1();
else
someOtherClass.method2();
}
}
public class SomeOtherClass {
public void method1() {}
public void method2() {}
}
If you want to test a.method will invoke a method from SomeOtherClass, you can write something like below.
#Test
public void testPrivateMemberMethodCalled() {
A a = new A();
SomeOtherClass someOtherClass = Mockito.spy(new SomeOtherClass());
ReflectionTestUtils.setField( a, "someOtherClass", someOtherClass);
a.method( true );
Mockito.verify( someOtherClass, Mockito.times( 1 ) ).method1();
}
ReflectionTestUtils.setField(); will stub the private member with something you can spy on.

I don't really understand your need to test the private method. The root problem is that your public method has void as return type, and hence you are not able to test your public method. Hence you are forced to test your private method. Is my guess correct??
A few possible solutions (AFAIK):
Mocking your private methods, but still you won't be "actually" testing your methods.
Verify the state of object used in the method. MOSTLY methods either do some processing of the input values and return an output, or change the state of the objects. Testing the objects for the desired state can also be employed.
public class A{
SomeClass classObj = null;
public void publicMethod(){
privateMethod();
}
private void privateMethod(){
classObj = new SomeClass();
}
}
[Here you can test for the private method, by checking the state change of the classObj from null to not null.]
Refactor your code a little (Hope this is not a legacy code). My funda of writing a method is that, one should always return something (a int/ a boolean). The returned value MAY or MAY NOT be used by the implementation, but it will SURELY BE used by the test
code.
public class A
{
public int method(boolean b)
{
int nReturn = 0;
if (b == true)
nReturn = method1();
else
nReturn = method2();
}
private int method1() {}
private int method2() {}
}

Put your test in the same package, but a different source folder (src/main/java vs. src/test/java) and make those methods package-private. Imo testability is more important than privacy.

In cases where the private method is not void and the return value is used as a parameter to an external dependency's method, you can mock the dependency and use an ArgumentCaptor to capture the return value.
For example:
ArgumentCaptor<ByteArrayOutputStream> csvOutputCaptor = ArgumentCaptor.forClass(ByteArrayOutputStream.class);
//Do your thing..
verify(this.awsService).uploadFile(csvOutputCaptor.capture());
....
assertEquals(csvOutputCaptor.getValue().toString(), "blabla");

Building on #aravind-yarram's answer: Not possible through mockito. From their wiki
So what's the OO way of testing private methods? Private methods with complex logic might be a sign that your class is violating the principle of single responsibility and that some of the logic should be moved to a new class.
Indeed, by extracting those private methods to public methods of more granular classes, you can unit test them without breaking the encapsulation of your original class.