Simple Guice & JUnit4 Integration: Use the unit test itself as a module to provide member injection. Use @provides methods to build a module from unit test object.

AuthenService.java

import com.google.inject.Inject;


public class AuthenService {

    private final UserDAO userDAO;

    @Inject
    public AuthenService(UserDAO userDAO) {
        this.userDAO = userDAO;
    }

    public User login(String username, String password) throws AuthenticationException {
        User user = userDAO.findUser(username);
        if (user == null) {
            throw new UserNotFoundException();
        }

        // TODO: Hash password before compare
        if (!user.getPassword().equals(password)) {
            throw new PasswordDontMatchException();
        }

        if (!user.isActive()) {
            throw new NotActiveException();
        }

        return user;
    }

}

EasyMockTest.java

import com.google.inject.Inject;
import com.google.inject.Provides;
import com.google.inject.Singleton;
import junit.framework.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;

import static org.easymock.EasyMock.*;

@RunWith(GuiceJUnit4Runner.class)
public class EasyMockTest {

    @Inject private AuthenService authenService;
    @Inject private UserDAO userDAO;

    @Provides @Singleton
    public UserDAO mockUserDAO() {
        return createStrictMock(UserDAO.class);
    }

    @Test
    public void successLogin() {
        User virasak = new User();
        virasak.setUsername("virasak");
        virasak.setPassword("123456");
        virasak.setActive(true);

        expect(userDAO.findUser(eq(virasak.getUsername()))).andReturn(virasak);
        replay(userDAO);

        try {
            User loginUser = authenService.login(virasak.getUsername(), virasak.getPassword());
            Assert.assertEquals(loginUser, virasak);
            verify(userDAO);
        } catch (AuthenticationException e) {}
    }
}

GuiceJUnit4Runner.java

import com.google.inject.Guice;
import com.google.inject.Module;
import com.google.inject.internal.ProviderMethodsModule;
import org.junit.runners.BlockJUnit4ClassRunner;
import org.junit.runners.model.InitializationError;

public class GuiceJUnit4Runner extends BlockJUnit4ClassRunner {

    public GuiceJUnit4Runner(Class<?> klass) throws InitializationError {
        super(klass);
    }

    @Override
    public Object createTest() throws Exception {
        Object object = super.createTest();
        Module module = ProviderMethodsModule.forObject(object);
        Guice.createInjector(module).injectMembers(object);
        return object;
    }

}

SimpleInjectTest.java

package com.googlecode.guicejunit4;

import com.google.inject.Inject;
import com.google.inject.Provides;
import com.google.inject.name.Named;
import static junit.framework.Assert.*;
import org.junit.Test;
import org.junit.runner.RunWith;

@RunWith(GuiceJUnit4Runner.class)
public class SimpleInjectTest {

    @Inject
    private SimpleService simpleService;

    @Provides @Named("greeter")
    String greeter() {
        return "Hello World";
    }

    @Test
    public void testInject() {
        assertNotNull(simpleService);
    }

    @Test
    public void testInjectDependencies() {
        assertEquals(simpleService.getGreeter(), "Hello World");
    }
}

SimpleService.java

package com.googlecode.guicejunit4;

import com.google.inject.Inject;
import com.google.inject.name.Named;

public class SimpleService {

    @Inject @Named("greeter")
    private String greeter;

    public String getGreeter() {
        return greeter;
    }
}

User.java

public class User {
    private long userId;
    private String username;
    private String password;
    private boolean active;

    public long getUserId() {
        return userId;
    }

    public void setUserId(long userId) {
        this.userId = userId;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public boolean isActive() {
        return active;
    }

    public void setActive(boolean active) {
        this.active = active;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }
}

UserDAO.java

public interface UserDAO {
    User findUser(String userName);
}