I've written a factory to produce java.sql.Connection objects:
public class MySQLDatabaseConnectionFactory implements DatabaseConnectionFactory {
#Override public Connection getConnection() {
try {
return DriverManager.getConnection(...);
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
}
I'd like to validate the parameters passed to DriverManager.getConnection, but I don't know how to mock a static method. I'm using JUnit 4 and Mockito for my test cases. Is there a good way to mock/verify this specific use-case?
Use PowerMockito on top of Mockito.
Example code:
#RunWith(PowerMockRunner.class)
#PrepareForTest(DriverManager.class)
public class Mocker {
#Test
public void shouldVerifyParameters() throws Exception {
//given
PowerMockito.mockStatic(DriverManager.class);
BDDMockito.given(DriverManager.getConnection(...)).willReturn(...);
//when
sut.execute(); // System Under Test (sut)
//then
PowerMockito.verifyStatic();
DriverManager.getConnection(...);
}
More information:
Why doesn't Mockito mock static methods?
Mocking of static methods in Mockito is possible since Mockito 3.4.0.
For more details see:
https://github.com/mockito/mockito/releases/tag/v3.4.0
https://github.com/mockito/mockito/issues/1013
https://javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#static_mocks
assertEquals("foo", Foo.method());
try (MockedStatic mocked = mockStatic(Foo.class)) {
mocked.when(Foo::method).thenReturn("bar");
assertEquals("bar", Foo.method());
mocked.verify(Foo::method);
}
assertEquals("foo", Foo.method());
In your case, something like this:
#Test
public void testStaticMockWithVerification() throws SQLException {
try (MockedStatic<DriverManager> dummy = Mockito.mockStatic(DriverManager.class)) {
DatabaseConnectionFactory factory = new MySQLDatabaseConnectionFactory();
dummy.when(() -> DriverManager.getConnection("arg1", "arg2", "arg3"))
.thenReturn(new Connection() {/*...*/});
factory.getConnection();
dummy.verify(() -> DriverManager.getConnection(eq("arg1"), eq("arg2"), eq("arg3")));
}
}
NOTE: mocking STATIC METHODS requires mockito-inline dependency instead of mockito-core.
For JUnit5 also add this:
<dependency>
<groupId>org.mockito</groupId>
<artifactId>mockito-junit-jupiter</artifactId>
<version>${mockito.version}</version>
<scope>test</scope>
</dependency>
The typical strategy for dodging static methods that you have no way of avoiding using, is by creating wrapped objects and using the wrapper objects instead.
The wrapper objects become facades to the real static classes, and you do not test those.
A wrapper object could be something like
public class Slf4jMdcWrapper {
public static final Slf4jMdcWrapper SINGLETON = new Slf4jMdcWrapper();
public String myApisToTheSaticMethodsInSlf4jMdcStaticUtilityClass() {
return MDC.getWhateverIWant();
}
}
Finally, your class under test can use this singleton object by, for example,
having a default constructor for real life use:
public class SomeClassUnderTest {
final Slf4jMdcWrapper myMockableObject;
/** constructor used by CDI or whatever real life use case */
public myClassUnderTestContructor() {
this.myMockableObject = Slf4jMdcWrapper.SINGLETON;
}
/** constructor used in tests*/
myClassUnderTestContructor(Slf4jMdcWrapper myMock) {
this.myMockableObject = myMock;
}
}
And here you have a class that can easily be tested, because you do not directly use a class with static methods.
If you are using CDI and can make use of the #Inject annotation then it is even easier.
Just make your Wrapper bean #ApplicationScoped, get that thing injected as a collaborator (you do not even need messy constructors for testing), and go on with the mocking.
I had a similar issue. The accepted answer did not work for me, until I made the change: #PrepareForTest(TheClassThatContainsStaticMethod.class), according to PowerMock's documentation for mockStatic.
And I don't have to use BDDMockito.
My class:
public class SmokeRouteBuilder {
public static String smokeMessageId() {
try {
return InetAddress.getLocalHost().getHostAddress();
} catch (UnknownHostException e) {
log.error("Exception occurred while fetching localhost address", e);
return UUID.randomUUID().toString();
}
}
}
My test class:
#RunWith(PowerMockRunner.class)
#PrepareForTest(SmokeRouteBuilder.class)
public class SmokeRouteBuilderTest {
#Test
public void testSmokeMessageId_exception() throws UnknownHostException {
UUID id = UUID.randomUUID();
mockStatic(InetAddress.class);
mockStatic(UUID.class);
when(InetAddress.getLocalHost()).thenThrow(UnknownHostException.class);
when(UUID.randomUUID()).thenReturn(id);
assertEquals(id.toString(), SmokeRouteBuilder.smokeMessageId());
}
}
As mentioned before you can not mock static methods with mockito.
If changing your testing framework is not an option you can do the following:
Create an interface for DriverManager, mock this interface, inject it via some kind of dependency injection and verify on that mock.
For those who use JUnit 5, Powermock is not an option. You'll require the following dependencies to successfully mock a static method with just Mockito.
testCompile group: 'org.mockito', name: 'mockito-core', version: '3.6.0'
testCompile group: 'org.mockito', name: 'mockito-junit-jupiter', version: '3.6.0'
testCompile group: 'org.mockito', name: 'mockito-inline', version: '3.6.0'
mockito-junit-jupiter add supports for JUnit 5.
And support for mocking static methods is provided by mockito-inline dependency.
Example:
#Test
void returnUtilTest() {
assertEquals("foo", UtilClass.staticMethod("foo"));
try (MockedStatic<UtilClass> classMock = mockStatic(UtilClass.class)) {
classMock.when(() -> UtilClass.staticMethod("foo")).thenReturn("bar");
assertEquals("bar", UtilClass.staticMethod("foo"));
}
assertEquals("foo", UtilClass.staticMethod("foo"));
}
The try-with-resource block is used to make the static mock remains temporary, so it's mocked only within that scope.
When not using a try block, make sure to close the mock, once you are done with the assertions.
MockedStatic<UtilClass> classMock = mockStatic(UtilClass.class)
classMock.when(() -> UtilClass.staticMethod("foo")).thenReturn("bar");
assertEquals("bar", UtilClass.staticMethod("foo"));
classMock.close();
Mocking void methods:
When mockStatic is called on a class, all the static void methods in that class automatically get mocked to doNothing().
Observation : When you call static method within a static entity, you need to change the class in #PrepareForTest.
For e.g. :
securityAlgo = MessageDigest.getInstance(SECURITY_ALGORITHM);
For the above code if you need to mock MessageDigest class, use
#PrepareForTest(MessageDigest.class)
While if you have something like below :
public class CustomObjectRule {
object = DatatypeConverter.printHexBinary(MessageDigest.getInstance(SECURITY_ALGORITHM)
.digest(message.getBytes(ENCODING)));
}
then, you'd need to prepare the class this code resides in.
#PrepareForTest(CustomObjectRule.class)
And then mock the method :
PowerMockito.mockStatic(MessageDigest.class);
PowerMockito.when(MessageDigest.getInstance(Mockito.anyString()))
.thenThrow(new RuntimeException());
You can do it with a little bit of refactoring:
public class MySQLDatabaseConnectionFactory implements DatabaseConnectionFactory {
#Override public Connection getConnection() {
try {
return _getConnection(...some params...);
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
//method to forward parameters, enabling mocking, extension, etc
Connection _getConnection(...some params...) throws SQLException {
return DriverManager.getConnection(...some params...);
}
}
Then you can extend your class MySQLDatabaseConnectionFactory to return a mocked connection, do assertions on the parameters, etc.
The extended class can reside within the test case, if it's located in the same package (which I encourage you to do)
public class MockedConnectionFactory extends MySQLDatabaseConnectionFactory {
Connection _getConnection(...some params...) throws SQLException {
if (some param != something) throw new InvalidParameterException();
//consider mocking some methods with when(yourMock.something()).thenReturn(value)
return Mockito.mock(Connection.class);
}
}
I also wrote a combination of Mockito and AspectJ: https://github.com/iirekm/varia/tree/develop/ajmock
Your example becomes:
when(() -> DriverManager.getConnection(...)).thenReturn(...);
Mockito cannot capture static methods, but since Mockito 2.14.0 you can simulate it by creating invocation instances of static methods.
Example (extracted from their tests):
public class StaticMockingExperimentTest extends TestBase {
Foo mock = Mockito.mock(Foo.class);
MockHandler handler = Mockito.mockingDetails(mock).getMockHandler();
Method staticMethod;
InvocationFactory.RealMethodBehavior realMethod = new InvocationFactory.RealMethodBehavior() {
#Override
public Object call() throws Throwable {
return null;
}
};
#Before
public void before() throws Throwable {
staticMethod = Foo.class.getDeclaredMethod("staticMethod", String.class);
}
#Test
public void verify_static_method() throws Throwable {
//register staticMethod call on mock
Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
"some arg");
handler.handle(invocation);
//verify staticMethod on mock
//Mockito cannot capture static methods so we will simulate this scenario in 3 steps:
//1. Call standard 'verify' method. Internally, it will add verificationMode to the thread local state.
// Effectively, we indicate to Mockito that right now we are about to verify a method call on this mock.
verify(mock);
//2. Create the invocation instance using the new public API
// Mockito cannot capture static methods but we can create an invocation instance of that static invocation
Invocation verification = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
"some arg");
//3. Make Mockito handle the static method invocation
// Mockito will find verification mode in thread local state and will try verify the invocation
handler.handle(verification);
//verify zero times, method with different argument
verify(mock, times(0));
Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
"different arg");
handler.handle(differentArg);
}
#Test
public void stubbing_static_method() throws Throwable {
//register staticMethod call on mock
Invocation invocation = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
"foo");
handler.handle(invocation);
//register stubbing
when(null).thenReturn("hey");
//validate stubbed return value
assertEquals("hey", handler.handle(invocation));
assertEquals("hey", handler.handle(invocation));
//default null value is returned if invoked with different argument
Invocation differentArg = Mockito.framework().getInvocationFactory().createInvocation(mock, withSettings().build(Foo.class), staticMethod, realMethod,
"different arg");
assertEquals(null, handler.handle(differentArg));
}
static class Foo {
private final String arg;
public Foo(String arg) {
this.arg = arg;
}
public static String staticMethod(String arg) {
return "";
}
#Override
public String toString() {
return "foo:" + arg;
}
}
}
Their goal is not to directly support static mocking, but to improve its public APIs so that other libraries, like Powermockito, don't have to rely on internal APIs or directly have to duplicate some Mockito code. (source)
Disclaimer: Mockito team thinks that the road to hell is paved with static methods. However, Mockito's job is not to protect your code from static methods. If you don’t like your team doing static mocking, stop using Powermockito in your organization. Mockito needs to evolve as a toolkit with an opinionated vision on how Java tests should be written (e.g. don't mock statics!!!). However, Mockito is not dogmatic. We don't want to block unrecommended use cases like static mocking. It's just not our job.
To mock static method you should use a Powermock look at:
https://github.com/powermock/powermock/wiki/MockStatic.
Mockito doesn't provide this functionality.
You can read nice a article about mockito:
http://refcardz.dzone.com/refcardz/mockito
I found one solution in Mockito. This feature comes with a version only from 3.4.0
https://asolntsev.github.io/en/2020/07/11/mockito-static-methods/
dependency
In your build.gradle replace mockito-core:3.3.3 by mockito-inline:3.4.0:
testImplementation('org.mockito:mockito-inline:3.4.0')
what are we going to mock
class Buddy
{
static String name()
{
return "John";
}
}
Mock the static method
#Test
void lookMomICanMockStaticMethods()
{
assertThat(Buddy.name()).isEqualTo("John");
try (MockedStatic<Buddy> theMock = Mockito.mockStatic(Buddy.class))
{
theMock.when(Buddy::name).thenReturn("Rafael");
assertThat(Buddy.name()).isEqualTo("Rafael");
}
assertThat(Buddy.name()).isEqualTo("John");
}
I think this could help us.
Since that method is static, it already has everything you need to use it, so it defeats the purpose of mocking.
Mocking the static methods is considered to be a bad practice.
If you try to do that, it means there is something wrong with the way you want to perform testing.
Of course you can use PowerMockito or any other framework capable of doing that, but try to rethink your approach.
For example: try to mock/provide the objects, which that static method consumes instead.
When you try to mock the static method, you have to write the test inside the try block. because It's important to note that scoped mocks must be closed by the entity that activates the mock.
try (MockedStatic<Tester> tester = Mockito.mockStatic(Tester.class)) {
tester.when(() -> Tester.testStatic("Testing..")).thenReturn(mock(ReturnObject.class));
//Here you have to write the test cases
}
In the above example, we have to mock the Tester Class testStatic Method with input param as "Testing...". Here, this method will return a ReturnObject class type object. Hence we write mockito when chain like above.
Don't forget to add below dependency in your Gradle/maven
testImplementation 'org.mockito:mockito-inline:4.3.1'
Use JMockit framework. It worked for me. You don't have to write statements for mocking DBConenction.getConnection() method. Just the below code is enough.
#Mock below is mockit.Mock package
Connection jdbcConnection = Mockito.mock(Connection.class);
MockUp<DBConnection> mockUp = new MockUp<DBConnection>() {
DBConnection singleton = new DBConnection();
#Mock
public DBConnection getInstance() {
return singleton;
}
#Mock
public Connection getConnection() {
return jdbcConnection;
}
};
There is an easy solution by using java FunctionalInterface and then add that interface as dependency for the class you are trying to unit test.
For mocking static functions i was able to do it that way:
create a wrapper function in some helper class/object. (using a name variant might be beneficial for keeping things separated and maintainable.)
use this wrapper in your codes. (Yes, codes need to be realized with testing in mind.)
mock the wrapper function.
wrapper code snippet (not really functional, just for illustration)
class myWrapperClass ...
def myWrapperFunction (...) {
return theOriginalFunction (...)
}
of course having multiple such functions accumulated in a single wrapper class might be beneficial in terms of code reuse.
Here I share my mockito MockStatic solution based on an extension as promised in my answer to leokom's solution.
So, why does Mockito choose try-with-resources? Well, simply because they want to keep a tidy ship. That is good programming after all. Try-with-resources allows construction with guaranteed calling of the close method. But in JUnit we already have that in BeforeEach and AfterEach. And one can easily add these for a generic purpose to each test class using an Extension that implements BeforeEachCallback and AfterEachCallback.
So much for the theory. Let's make a static mock for
Instant.now()
I started with an annotation to be able to mark the fields in my test class that I want to use as static mocks.
#Retention(RetentionPolicy.RUNTIME)
#Target(ElementType.FIELD)
public #interface StaticMock {
}
This allows me to create a field in my test class for static mocking that I can easily find in my Extension class.
#StaticMock
private MockedStatic<Instant> staticInstantMock;
I added the Extension I created to my test class. You have two options.
Create an Extension for this purpose and add it to the class next to MockitoExtension, which you also need.
Create an Extension and have it inherit from MockitoExtension. Now you can replace MockitoExtension on your test class.
I used the latter of the two.
#ExtendWith({CompanyMockitoExtension.class})
class MyExtendedTestClass {
Now we need something to be returned for the static when it's called:
#Mock
private Instant now;
staticInstantMock.when(Instant::now).thenReturn(now);
The whole test class:
#ExtendWith({CompanyMockitoExtension.class})
class MyExtendedTestClass {
#StaticMock
private MockedStatic<Instant> staticInstantMock;
#Mock
private Instant now;
#Test
void myTestMethod() {
staticInstantMock.when(Instant::now).thenReturn(now);
assertThat(Instant::now).isSameAs(now); // This would normally happen in the class you are testing...
}
}
Now let's take a look at the Extension class.
import static org.mockito.Mockito.mockStatic;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.List;
import org.junit.jupiter.api.extension.ExtensionContext;
import org.mockito.MockedStatic;
import org.mockito.Mockito;
import org.mockito.junit.jupiter.MockitoExtension;
public class CompanyMockitoExtension extends MockitoExtension {
#Override
public void beforeEach(ExtensionContext context) {
super.beforeEach(context); // Don't forget to call the super!!
if (context.getTestInstance().isEmpty()) { // Just to be sure...
return;
}
// Get the unit test instance
Object testSubject = context.getTestInstance().get();
initializeStaticMocks(testSubject);
}
private void initializeStaticMocks(Object testSubject) {
// Find all fields that I want to static mock
List<Field> staticMockFields = ReflectionHelper.getFieldsWithAnnotation(testSubject, StaticMock.class);
staticMockFields.forEach(field -> initializeStaticMock(field, testSubject));
}
private void initializeStaticMock(Field field, Object testSubject) {
// Get the type of the static mock. It is within the generic MockedStatic<> class type.
Class<?> typeForStaticMock = (Class<?>) ReflectionHelper.getTypesForGeneric(field)[0];
try {
// Now set the field with the mockStatic method of Mockito.
field.setAccessible(true);
field.set(testSubject, mockStatic(typeForStaticMock));
} catch (IllegalAccessException e) {
throw new RuntimeException("Failed to instantiate Static Mock with type: " + typeForStaticMock.getName());
}
}
#Override
public void afterEach(ExtensionContext context) {
super.afterEach(context); // Again, do not forget to call the super.
if (context.getTestInstance().isEmpty()) {
return;
}
Object testSubject = context.getTestInstance().get();
closeStaticMocks(testSubject); // Close all static mocks.
}
private void closeStaticMocks(Object testSubject) {
// Again find all fields we annotated
List<Field> staticMockFields = ReflectionHelper.getFieldsWithAnnotation(testSubject, StaticMock.class);
staticMockFields.forEach(field -> closeStaticMock(field, testSubject));
}
private void closeStaticMock(Field field, Object testSubject) {
// Get the instance and simply call close.
MockedStatic<?> mockedStaticInstance = ReflectionHelper.getFieldInstance(field, testSubject, MockedStatic.class);
mockedStaticInstance.close();
}
}
The nice thing about this extension is that you can add additional mocking stuff. I added verification of no more interactions on all mocks in the AfterEach. This is now automatic when we use this extension. I also added similar behavior for construction mocking as for the static mocking.
As you see, I made my own reflection helper class. I know there are some standard reflection helper classes and those might be better. Here is mine for this purpose.
public class ReflectionHelper {
public static List<Field> getFieldsWithAnnotation(
Object testSubject,
Class<? extends Annotation> annotationType
) {
Class<?> testSubjectClass = testSubject.getClass();
return Arrays.stream(testSubjectClass.getDeclaredFields())
.filter(field -> field.isAnnotationPresent(annotationType))
.collect(toUnmodifiableList());
}
public static List<Field> getCollectionFields(Object testSubject) {
Class<?> testSubjectClass = testSubject.getClass();
return Arrays.stream(testSubjectClass.getDeclaredFields())
.filter(field -> Collection.class.isAssignableFrom(field.getType()))
.collect(toUnmodifiableList());
}
#SuppressWarnings("unchecked")
public static <T> T getFieldInstance(Field field, Object testSubject, Class<T> type) {
return (T) getFieldInstance(field, testSubject);
}
public static Object getFieldInstance(Field field, Object testSubject) {
try {
boolean isStatic = isStatic(field.getModifiers());
Object context = isStatic ? null : testSubject;
field.setAccessible(true);
return field.get(context);
} catch (IllegalAccessException e) {
throw new RuntimeException("Failed to get instance of field.");
}
}
public static Type[] getTypesForGeneric(Field field) {
ParameterizedType parameterizedType = (ParameterizedType) field.getGenericType();
return parameterizedType.getActualTypeArguments();
}
}
Refactor it a little bit:
public class MySQLDatabaseConnectionFactory implements DatabaseConnectionFactory {
ConnectionSupplier connectionSupplier = () -> SupplierDriverManager.getConnection();
public void setConnSupplier(ConnectionSupplier supplier) {
this.connectionSupplier = supplier;
}
#Override
public Connection getConnection() {
try {
return connectionSupplier.conn();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
#FunctionalInterface
interface ConnectionSupplier {
Connection conn();
}
}
Then you can use the mockito:
MySQLDatabaseConnectionFactory.ConnectionSupplier connectionSupplier = mock(MySQLDatabaseConnectionFactory.ConnectionSupplier.class);
when(connectionSupplier.conn()).thenReturn(yourMockObject);
yourConnectionFactory.setConnSupplier(connectionSupplier);
Related
I'm trying to test a method that calls an external util static method for a check, and need to somehow mock it to return true / false conditions, here is a sample:
class foo {
public void methodToTest(){
..logic
boolean myCondition = SomeUtil.checkCondition(args);
..more logic
}
}
Is this possible to do with mockito only? If not directly, is there a way to replace the SameUtil method with reflection or something similar?
I saw people suggesting powermock, but they don't have mockito 3.x listed on their compatibility chart, is there a better option?
This seems like a pretty common case, not everything should be autowired or injected.
Option 1: factor out the static method call into a separate method and use Mockito spy:
class Foo {
public void methodToTest(){
checkCondition(args);
// ....
}
boolean checkCondition(Object args) {
return SomeUtil.checkCondition(args);
}
}
class FooTest {
#Spy
#InjectMocks
private Foo foo;
#Test
void methodToTest() {
//...
when(foo.checkCondition(yourArg)).thenReturn(true);
}
}
See the Spy documentation for more details:
Option 2: factor out verification into a class:
class ArgumentVerifier {
boolean checkArgument(Object args) {
return SomeUtil.checkCondition(args);
}
}
class Foo {
private ArgumentVerifier verifier;
public void methodToTest() {
verifier.checkArgument(args); // mock the verifier as you normally would
// ....
}
}
It is possible since Mockito 3.4.0: Mocking Static Methods With Mockito
But please be aware that:
injecting remains a more explicit way of expressing dependency on another object/service, especially external api
static helper methods rarely need to be mocked (especially if they depend only on their arguments)
This limits the number of cases where mocking a static method is the tool of choice, but it is worth having it under your belt.
I have a test case that mock a static method of java.lang.System class:
#Test
fun `getLocalTime()`() {
// Arrange
val staticMock = Mockito.mockStatic(System::class.java)
Mockito.`when`(System.currentTimeMillis()).thenReturn(1000L)
// Action
val res = deviceTimeProvider.getLocalTime()
// Assert
Truth.assertThat(res).isEqualTo(1000L)
staticMock.close()
}
But when I run the test, I got this error:
org.mockito.exceptions.base.MockitoException: It is not possible to
mock static methods of java.lang.System to avoid interfering with
class loading what leads to infinite loops
Why does this happen? How can I mock methods of java.lang.System class?
While Mockito since 3.4.0 version allows mocking static methods it is not allowed to mock the Thread and System static methods, see this comment on github
Finally note that Mockito forbids mocking the static methods of System (and Thread). Those methods are to much cemented into class loading which happens in the same thread. At some point, we might add instrumentation to class loading to temporarily disable the static mocks within it to make mocking these classes, too, where we also would need to disable their intensification properties. You can however easily mock Instant.now().
If you like ugly solutions you can still mock System with PowerMockito
#PrepareForTest(System.class)
public class TestCase {
#BeforeClass
public void setup() {
PowerMockito.mockStatic(System.class);
PowerMockito.when(System.currentTimeMillis()).thenReturn(1000L);
}
...
But I would avoid mocking System classes if possible. You can still wrap it in method and mock this method.
To mock the static methods of java.lang.System class with the help of Mockito.
Create an interface i.e ISystem.java
public interface ISystem {
String getProperty(String name);
Long getCurrentTimeInMillis();
}
2- Create the implementation class of ISystem interface i.e ISystemImpl.java
public class ISystemImpl implements ISystem {
#Override
public String getProperty(final String name) {
return System.getProperty(name);
}
#Override
public Long getCurrentTimeInMillis() {
return System.currentTimeMillis();
}
}
3- Use Isystem.java inside your DeviceTimeProvider.java class.
public class DeviceTimeProvider {
#NonNull private final ISystem mISystem;
public DeviceTimeProvider(ISystem iSystem){
mIsystem = iSystem;
}
public Long getLocalTime(){
return mIsystem.getCurrentTimeInMillis()
}
}
4- Now finally mock the ISystem interface inside your test class.
public class DeviceTimeProviderTest {
private ISystem mISystem;
private DeviceTimeProvider sut;
#Before
public setup(){
mIsystem = mockito.mock(ISystem.class)
sut = new DeviceTimeProvider(mISystem);
}
#Test
public void getDeviceLocalTime(){
Long expectedTime = 1000L;
mockit.when(mISystem.getCurrentTimeInMillis()).thenReturn(expectedTime);
Long actualTime = sut.getLocalTime();
Assert.assertEquals(actualTime, expectedTime);
}
}
OUTPUT
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!
How can I override an object creation inside a method?
public class ClassToTest {
public Object testMethod() {
... code ...
Object result;
try {
result = new ClassToMock(someParam).execute();
} catch (Exception e) {
// handle error
}
return result;
}
}
How can my test override the "execute" method of ClassToMock? I will be happy for code examples with EasyMock. I want to test "testMethod", something like:
#Test
public void testMethodTest(){
ClassToTest tested = new ClassToTest();
// Mock ClassToMock somehow
tested.testMethod();
// Verify results
}
Simply spoken: that doesn't work.
You can't mock calls to new (using EasyMock. It is possible using frameworks like PowerMock(ito) or JMockit though).
But the better way: use dependency injection in order to pass already created objects into your class under test.
To be more precise: if your class really doesn't need any other objects to work, then a test would more look like
#Test
public void testFoo() {
ClassToTest underTest = new ClassToTest(...)
underTest.methodToTest();
assertThat( ... )
In other words: in order to test your class, you simply instantiate it; then you call methods on it; and you use asserts to check the expected states of it.
See here for excellent (although a bit lengthy) explanations on what I am talking about.
It is only possible to override methods if the method of the class is not marked as final
try {
ClassToMock mock = new ClassToMock(someParam){
public Object execute(){ //Such that your method is public
//If you want to call back to the pure method
//super.execute()
//Do override things here
}
};
result = mock.execute();
} catch (Exception e) {
// handle error
}
It is possible with Powermock. Using powermock, you can mock 'new' operator as well
ClassToMock mock = PowerMock.createMock(ClassToMock.class);
PowerMock.expectNew(ClassToMock.class, parameterValues).andReturn(mock);
PowerMock.replayAll();
For more details please refer this link
I am new to mocking and so I'm playing around with this scenario. I have a method MyClass.process() which calls MyClass.getFactory(). I want to mock getFactory() to fail so that I can assure process() recovers correctly.
It seems that if I call getFactory() after the mock it throws the exception correctly, but if it is called through the original process() method the exception is not thrown.
public class MyClass {
public MyFactory getFactory() throws FactoryException {
return ...
}
public String process() {
try {
MyFactory factory = getFactory();
...
}
catch(FactoryException ex) {
...
}
}
}
Test class:
public class MyClassTest {
#Test
public void testGetFactoryFails() {
try {
MyClass mockMyClass = mock(MyClass.class);
when(mockMyClass.getFactory()).thenThrow(new FactoryException());
mockMyClass.process();
fail("FactoryException should have been thrown.");
}
catch(FactoryException ex) {
// all good
}
}
}
Thanks for all the feedback. I can see how mocking single methods under more complex environments would quickly become unmanageable. The contents of getFactory() is not important as this is concept code, not production code.
One way I tried that works well:
public class MyClassTest {
class MyClassMock1 extends MyClass {
#Override
public MyFactory getFactory() throws FactoryException {
throw new FactoryException("Bad factory instance.");
}
}
#Test
public void testGetFactoryFails() {
try {
MyClassMock1 mockMyClass = new MyClassMock1();
mockMyClass.process();
fail("FactoryException should have been thrown.");
}
catch(FactoryException ex) {
assertEquals("Bad factory instance.", ex.getMessage());
}
}
}
I'll expand what #Can't Tell already said. You use mocking library to mock dependencies of a class under test. In your case you test MyClass and during tests you should mock all the dependencies (classes that MyClass uses).
You want to mock a single method in one class and test another method. While this might be technically possible (but due to various proxying/wrapping mechanics it doesn't work for you), it's certainly a bad design.
Show us your getFactory() method. If it handles the whole work alone, extract it to a separate class and mock it. If it only delegates to another class, mock that one. Sadly, this extracted class will be named... MyFactoryFactory...
Once you get your dependency extracted, mock it and pass to MyClass before testing (via contstructor, setter...)
it's because partial mocking is BAD (and that's what you are trying to do). it leads exactly to those kind of problems. it's introduced mainly for legacy systems testing. if you write new code and you have to use partial mocking this mean you most probably have bad system design.
you should make getFactory delegate the invocation to some other service (injected into MyClass) and then you should mock the whole service