Junit Private Methods
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Junit private methods: How to unit test private methods and classes
Powermock is an open-source Java framework. Powermock leverages the capabilities of frameworks like Mockito to create mock objects in unit testing. Unit testing private methods and classes are possible by using Powermock's Whitebox. The Whitebox uses reflection to create inner class instances and invoke private methods outside the class file they are declared.
If you have been researching how to unit test private methods and classes, you may have come across various debates about best practices. I am confident that "Don't unit test private methods" is not the answer you want to find. If unit testing private methods and classes are inevitable for your situation, this article explains how to test private methods and classes.
org.powermock.reflect.Whitebox provides various utilities for accessing the internals of a class. These utilities include instantiating private classes and invoking private methods by using reflection. Whitebox is a utility intended for tests.
The below is the test candidate class with private methods and an inner class. Note that those methods and inner class are not accessible outside the class they are defined.
package com.learnbestcoding.junit;
import java.util.ArrayList;
import java.util.List;
public class Util
{
public void runMethods(String[] args)
{
//Public method uses all private methods
}
private static int getNumber()
{
return 1;
}
private List getLanguages()
{
List languages = new ArrayList();
languages.add("Java");
languages.add("Sql");
languages.add("Javascript");
return languages;
}
private void addLanguage(List languages, String language)
{
languages.add(language);
}
private ProgrammingLanguages getJavaLanguageClass()
{
ProgrammingLanguages languages = new ProgrammingLanguages();
languages.setLanguageId(1);
languages.setLanguageName("Java");
languages.setNoOfEnrolments(100);
return languages;
}
private ProgrammingLanguages createLanguageClass(int languageId, String languageName, int noOfEnrolments)
{
ProgrammingLanguages languages = new ProgrammingLanguages();
languages.setLanguageId(languageId);
languages.setLanguageName(languageName);
languages.setNoOfEnrolments(noOfEnrolments);
return languages;
}
private List addLanguageClass(ProgrammingLanguages language)
{
List languageList = new ArrayList();
languageList.add(language);
return languageList;
}
class ProgrammingLanguages{
int languageId;
String languageName;
int noOfEnrolments;
public int getLanguageId() {
return languageId;
}
public void setLanguageId(int languageId) {
this.languageId = languageId;
}
public String getLanguageName() {
return languageName;
}
public void setLanguageName(String languageName) {
this.languageName = languageName;
}
public int getNoOfEnrolments() {
return noOfEnrolments;
}
public void setNoOfEnrolments(int noOfEnrolments) {
this.noOfEnrolments = noOfEnrolments;
}
}
}
4.0.0
com.learnbestcoding
junit
0.0.1-SNAPSHOT
jar
junit
http://maven.apache.org
UTF-8
junit
junit
4.13.2
org.powermock
powermock-api-mockito
1.7.4
org.powermock
powermock-module-junit4
1.7.4
In this tutorial, we will discuss six different scenarios to test private classes and methods. These scenarios include simple private methods with no arguments to private methods that accept private class arguments and return private classes.
The private method getNumber() is a simple method without any arguments and returns 1 for every execution. The important thing is not the method logic but how you invoke this method outside the method scope. The below code illustrates how to invoke a private method with no arguments and a simple return value. The getNumber is the private method name in Util.java class and Whitebox.invokeMethod(new Util(),"getNumber") returns the method return value.
package com.learnbestcoding.junit;
import static org.junit.Assert.assertEquals;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.reflect.Whitebox;
@RunWith(PowerMockRunner.class)
public class UtilTest {
@Test
public void test_getNumber() throws Exception
{
int obj = Whitebox.invokeMethod(new Util(),"getNumber");
assertEquals(obj, 1);
}
}
The private method getLanguages() accepts no arguments and returns an ArrayList. The getLanguages is the private method name in Util.java class and Whitebox.invokeMethod(new Util(),"getLanguages") returns the method return value, which is an ArrayList.
@Test
public void test_getLanguages() throws Exception
{
List obj = Whitebox.invokeMethod(new Util(),"getLanguages");
assertEquals(obj.get(0), "Java");
}
The private method addLanguage() accepts two arguments and does not return a value. The addLanguage is the private method name in Util.java class, and method arguments are passed along with the method call Whitebox.invokeMethod(new Util(),"addLanguage",languages,"Python") The changes are mane to the variable reference languages.
@Test
public void test_addLanguage() throws Exception
{
List languages = new ArrayList();
languages.add("Java");
languages.add("Sql");
languages.add("Javascript");
Whitebox.invokeMethod(new Util(),"addLanguage",languages,"Python");
assertEquals(languages.get(3), "Python");
}
The private method getJavaLanguageClass() accepts no arguments and returns an inner class. Note that the test class has no access to the private method and inner class. The getJavaLanguageClass is the private method name in Util.java class, and ProgrammingLanguages is the inner class the method returns. Whitebox.invokeMethod(new Util(),"getJavaLanguageClass") returns the innerclass and we can access its methods with obj.getClass().getDeclaredField("languageId").get(obj). The languageId is the property name.
@Test
public void test_getLanguageClass() throws Exception
{
Object obj =Whitebox.invokeMethod(new Util(),"getJavaLanguageClass");
assertEquals(obj.getClass().getDeclaredField("languageId").get(obj), 1);
assertEquals(obj.getClass().getDeclaredField("languageName").get(obj), "Java");
assertEquals(obj.getClass().getDeclaredField("noOfEnrolments").get(obj), 100);
}
The private method createLanguageClass() accepts arguments and returns a private class. The createLanguageClass is the private method name in Util.java class, and ProgrammingLanguages is the inner class the method returns. Whitebox.invokeMethod(new Util(),"createLanguageClass",2,"Sql",240) passes the arguments to the private class and returns the return value of the private method. The return value is also a type of private class and the properties are accessible with obj.getClass().getDeclaredField("languageId").get(obj). The languageId is the class property name.
@Test
public void test_createLanguageClass() throws Exception
{
Object obj =Whitebox.invokeMethod(new Util(),"createLanguageClass",2,"Sql",240);
assertEquals(obj.getClass().getDeclaredField("languageId").get(obj), 2);
assertEquals(obj.getClass().getDeclaredField("languageName").get(obj), "Sql");
assertEquals(obj.getClass().getDeclaredField("noOfEnrolments").get(obj), 240);
}
The private method addLanguageClass() accepts private class as arguments and returns a private class. The addLanguageClass is the private method name in Util.java class, and ProgrammingLanguages is the inner class the method returns. Here is how to implement it.
@Test
public void test_addLanguageClass() throws Exception
{
Object programmingLanguages = new Object();
Class clazz = Whitebox.getInnerClassType(Util.class, "ProgrammingLanguages");
Constructor constructor = Whitebox.getConstructor(clazz,Util.class);
programmingLanguages = constructor.newInstance(new Util());
Field field = null;
field = programmingLanguages.getClass().getDeclaredField("languageId");
field.setAccessible(true);
field.set(programmingLanguages, 1);
field = programmingLanguages.getClass().getDeclaredField("languageName");
field.setAccessible(true);
field.set(programmingLanguages, "Java");
field = programmingLanguages.getClass().getDeclaredField("noOfEnrolments");
field.setAccessible(true);
field.set(programmingLanguages, 100);
List obj = Whitebox.invokeMethod(new Util(),"addLanguageClass",programmingLanguages);
assertEquals(obj.get(0).getClass().getDeclaredField("languageId").get(obj.get(0)), 1);
assertEquals(obj.get(0).getClass().getDeclaredField("languageName").get(obj.get(0)), "Java");
assertEquals(obj.get(0).getClass().getDeclaredField("noOfEnrolments").get(obj.get(0)), 100);
}
package com.learnbestcoding.junit;
import static org.junit.Assert.assertEquals;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.modules.junit4.PowerMockRunner;
import org.powermock.reflect.Whitebox;
@RunWith(PowerMockRunner.class)
public class UtilTest {
@Test
public void test_getNumber() throws Exception
{
int obj = Whitebox.invokeMethod(new Util(),"getNumber");
assertEquals(obj, 1);
}
@Test
public void test_getLanguages() throws Exception
{
List obj = Whitebox.invokeMethod(new Util(),"getLanguages");
assertEquals(obj.get(0), "Java");
}
@Test
public void test_addLanguage() throws Exception
{
List languages = new ArrayList();
languages.add("Java");
languages.add("Sql");
languages.add("Javascript");
Whitebox.invokeMethod(new Util(),"addLanguage",languages,"Python");
assertEquals(languages.get(3), "Python");
}
@Test
public void test_getLanguageClass() throws Exception
{
Object obj =Whitebox.invokeMethod(new Util(),"getJavaLanguageClass");
assertEquals(obj.getClass().getDeclaredField("languageId").get(obj), 1);
assertEquals(obj.getClass().getDeclaredField("languageName").get(obj), "Java");
assertEquals(obj.getClass().getDeclaredField("noOfEnrolments").get(obj), 100);
}
@Test
public void test_createLanguageClass() throws Exception
{
Object obj =Whitebox.invokeMethod(new Util(),"createLanguageClass",2,"Sql",240);
assertEquals(obj.getClass().getDeclaredField("languageId").get(obj), 2);
assertEquals(obj.getClass().getDeclaredField("languageName").get(obj), "Sql");
assertEquals(obj.getClass().getDeclaredField("noOfEnrolments").get(obj), 240);
}
@Test
public void test_addLanguageClass() throws Exception
{
Object programmingLanguages = new Object();
Class clazz = Whitebox.getInnerClassType(Util.class, "ProgrammingLanguages");
Constructor constructor = Whitebox.getConstructor(clazz,Util.class);
programmingLanguages = constructor.newInstance(new Util());
Field field = null;
field = programmingLanguages.getClass().getDeclaredField("languageId");
field.setAccessible(true);
field.set(programmingLanguages, 1);
field = programmingLanguages.getClass().getDeclaredField("languageName");
field.setAccessible(true);
field.set(programmingLanguages, "Java");
field = programmingLanguages.getClass().getDeclaredField("noOfEnrolments");
field.setAccessible(true);
field.set(programmingLanguages, 100);
List obj = Whitebox.invokeMethod(new Util(),"addLanguageClass",programmingLanguages);
assertEquals(obj.get(0).getClass().getDeclaredField("languageId").get(obj.get(0)), 1);
assertEquals(obj.get(0).getClass().getDeclaredField("languageName").get(obj.get(0)), "Java");
assertEquals(obj.get(0).getClass().getDeclaredField("noOfEnrolments").get(obj.get(0)), 100);
}
}
Powermock offers Whitebox utility offers utilities to unit test private methods and private classes using reflection. Whitebox makes private methods and classes accessible outside their defined scope and visibility.
Lance is a software engineer with over 15 years of experience in full-stack software development.
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How do you write a JUnit test for private methods?
Asked By: Heydi Caldeiro | Last Updated: 18th May, 2020
Category: technology and computing programming languages
So whether you are using JUnit or SuiteRunner, you have the same four basic approaches to testing private methods:
Don't test private methods.
Give the methods package access.
Use a nested test class.
Use reflection.
In Java you can write tests itself in the class to be tested and your test methods should be able to call private methods as well. Now you have access to protected methods and can unit test them (JUnit or TestNG doesnt really matter), yet you keep these methods from callers you did not want.
Secondly, can we write test cases for private methods? You generally don't unit test private methods directly. Since they are private, consider them an implementation detail. Nobody is ever going to call one of them and expect it to work a particular way. You should instead test your public interface.
Hereof, how do you write unit tests for private methods?
Unit test only the publicly available API. When writing unit tests, mimic the behavior of the SUT's clients. Don't test private methods. Either unit test them indirectly, using the public API, or extract them into separate classes and test those classes instead.
How do you make a private method visible in a Test class in Java?
To “just call it” in Java we need to change visibility of the method. The first way is to make method package private (no access modifier) and put tests into the same package. This is a fairly common practice, but you still might want (or already have) another code structure. The second way is to make method public.
Though private methods or variables are not accessible outside of Class. They can be accessed via reflection by using setAccessible(true) and changing there private visibility. Private method can not be overridden in Java, not even inside inner classes.
To run a test, select the test class, right-click on it and select Run-as JUnit Test. This starts JUnit and executes all test methods in this class. Eclipse provides the Alt + Shift + X , T shortcut to run the test in the selected class.
JUnit is an open source Unit Testing Framework for JAVA. It is useful for Java Developers to write and run repeatable tests. As the name implies, it is used for Unit Testing of a small chunk of code. Developers who are following test-driven methodology must write and execute unit test first before any code.
There are four easy steps in setting up a test that mocks a static call:
Use the PowerMock JUnit runner: @RunWith(PowerMockRunner.
Declare the test class that we're mocking:
Tell PowerMock the name of the class that contains static methods:
Setup the expectations, telling PowerMock to expect a call to a static method:
JUnit is an open source framework, which is used for writing and running tests. Provides annotations to identify test methods. Provides assertions for testing expected results. Provides test runners for running tests.
What is JUnit Annotations? Annotation is a special form of syntactic meta-data that can be added to Java source code for better code readability and structure. Variables, parameters, packages, methods and classes can be annotated. Some of the JUnit annotations which can be useful are. Before.
Use the TestVisible annotation to allow test methods to access private or protected members of another class outside the test class. These members include methods, member variables, and inner classes. This annotation enables a more permissive access level for running tests only.
android.support.annotation.VisibleForTesting. Denotes that the class, method or field has its visibility relaxed, so that it is more widely visible than otherwise necessary to make code testable.
You can access the private methods of a class using java reflection package.
Step1 − Instantiate the Method class of the java. lang.
Step2 − Set the method accessible by passing value true to the setAccessible() method.
Step3 − Finally, invoke the method using the invoke() method.
Reflection in Java. Reflection is an API which is used to examine or modify the behavior of methods, classes, interfaces at runtime. Reflection gives us information about the class to which an object belongs and also the methods of that class which can be executed by using the object.
Yes, don't Test private methods. The idea of a unit test is to test the unit by its public 'API'. If you are finding you need to test a lot of private behavior, most likely you have a new 'class' hiding within the class you are trying to test, extract it and test it by its public interface.
To test a protected method using junit and mockito, in the test class (the class used to test the method), create a “child class” that extends the protagonist class and merely overrides the protagonist method to make it public so as to give access to the method to the test class, and then write tests against this child
Press Alt+Shift+X,T to run the test (or right-click, Run As > JUnit Test). If you want to rerun the same test method, just press Ctrl+F11.
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Junit Private Methods
