Testing Tips for Java Developers

Mockito

• Don’t mock too much, only mock directly dependence
• Steps: create mock:@Mock -> stubbing:when/thenReturn -> Verify: verify
• @Spy: used to wrap a real object. Every call, unless specified otherwise, is delegated to the object.

import static org.mockito.Mockito.*;
@RunWith(MockitoJUnitRunner.class)
// When can't use @RunWith, for example test class already extends another base class.
@Rule public MockitoRule mockitoRule = MockitoJUnit.rule();
// Annotations
@Mock
Mockito.mock(XX.class) // or
@Spy
@InjectMocks
@Captor

ArgumentCaptor<XClass> captor=ArgumentCaptor.forClass(XClass.class);
verify(mock).doSomething(capto.capture());
// Stubbing
when(mockObj.someMethod(0)).thenReturn("someThing");
when(mockObj.someMethod(1)).thenThrow(new RuntimeException());
when(instance.someMethod()).thenReturn(someValue);
thenThrow(Throwable)
thenCallRealMethod()

doReturn|Answer|Throw()

• Important gotcha on spying real objects!
• use doReturn|Answer|Throw() to stub spy object
• use doXXX on void methods

// spy instance field
Typex ox = Mockito.spy(anObject.aField);
anObject.aField = ox;

doReturn("some").when(spyObj).someMethod();

doCallRealMethod().when(instance).voidMethod();
doThrow(new Exception()).when(instance).voidMethod()

verify(mockObj, never()).someMethod(param);
verifyZeroInteractions(mock...);
verify(mockObj, atLeast(2)).someMethod();
verify(mockObj, times(3)).someMethod();

reset

• after reset

Mock chained calls

@Mock(answer = Answers.RETURNS_DEEP_STUBS)
SomeService service;

when(service.getX().getY()).thenReturn(Z);

Do different things when call multiple times

doReturn(null).doReturn(anotherInstance).when(mock).method();

Invalid use of argument matchers!

• When using matchers, all arguments have to be provided by matchers.

//incorrect: 
someMethod(anyObject(), "raw String"); 
// Should be
someMethod(anyObject(), eq("raw String"));

UnfinishedVerificationException: Missing method call for verify(mock)

• in verify, use any() for primitive arguments

Testing Servlet

when(request.getParameter("user")).thenReturn("userA");
verify(response).setContentType("plain/text");
verify(response).addHeader("headerA")).thenReturn("value");

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Hamcrest

• More Readable.
• Provides Better Failure Messages
• Type Safety
• hasItem, contains, containsInAnyOrder

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;
org.hamcrest.Matchers
containsString, startsWith, endsWith, equalTo,equalToIgnoringCase, equalToIgnoringWhitespace, isEmpty, isEmptyOrNull and stringContainsInOrder

assertThat(actual, containsString(expected));
assertThat(actual, nullValue());
assertThat(actual, notNullValue());

assertThat(subClass, instanceOf(BaseClass.class));

[TestNG]

• Testing with TestNG

Spring + JUnit

• docs
• JUnit 4.11 does not work with Spring Test framework

Using REST Assured to test http APIs

Response rsp = given().filter(sessionFilter).when().get(someUrl).then().statusCode(is(200))).extract().response()
Map importResult = rsp.as(Map[].class)[0];

assertThat(Boolean.valueOf(importResult.get("success").toString()), is(true));

randomizedtesting

@RunWith(RandomizedRunner.class)
@Seed("the-seed")
@com.carrotsearch.randomizedtesting.annotations.Repeat(iterations = 5)

---

Eclipse

• Eclipse Tips

Plugins

• MoreUnit
  • Ctrl+U: create test method
  • Ctrl+J: jump to test method

Add Static Import Automatically

• To help write test cases easier, when we type “assertT” and hit Ctrl+Space, we want Eclipse to add static import automatically for us: import static org.hamcrest.MatcherAssert.assertThat;
• Go to Window > Preferences > Java > Editor > Content Assist > Favorites, then add:

org.hamcrest
org.hamcrest.Matchers.*
org.hamcrest.CoreMatchers.*

org.junit.*
org.junit.Assert.*
org.junit.Assume.*
org.junit.matchers.JUnitMatchers.*

org.mockito.Mockito
org.mockito.Matchers
org.mockito.ArgumentMatchers
io.restassured.RestAssured

Run Tests across Multiple Projects

• Eclipse Tips + Tricks - 2016
• https://github.com/takari/takari-cpsuite

Create a maven project depending on all the projects you want to test.
Create Test code:

import org.junit.extensions.cpsuite.ClasspathSuite;
import org.junit.runner.RunWith;
@RunWith(ClasspathSuite.class)
public class TestRunner {
}

Maven

• Run specific method: mvn test -Dtest=className#methodName

Misc

• json-server - Get a full fake REST API Server
• Loading test
• JMeter
• Tsung
• locustio