JAAS / Kerberos stub with Mockito

November 14, 2020

What's inside this article ⌄

Mockito JAAS stub
Mock JAAS Mockito
JAAS unit tests
Mockito Kerberos stub
Mock Kerberos Mockito
Kerberos unit tests

Suppose we need to test the functionality of method X. It does the following things:

Performs authentication using JAAS
If authentication is successful, it continues to work

It’s often problematic to set up a working authentication mechanism in a unit test environment. One solution to the problem is to set a stub on the login() method of the LoginContext class.

Let’s say we have a class Tested that contains a method X:

class Tested {
    public String x() {
        LoginContext lc = new LoginContext(/*<special_parameters>*/);
        lc.login();
        // ...
        // <tested_functionality>
        // ...
    }
}

Connecting Mockito for Maven:

<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-core</artifactId>
    <version>2.16.0</version>
    <scope>test</scope>
</dependency>

For Gradle:

testCompile group: 'org.mockito', name: 'mockito-core', version: '2.16.0'

It will not be possible to control the created object of the LoginContext class in the current implementation of method X. Let’s move this creation into a new method createLoginContext(…) of the Tested class:

class Tested {
    public String x() {
        LoginContext lc = createLoginContext(/*<special_parameters>*/);
        lc.login();
        // ...
        // <tested_functionality>
        // ...
    }

    public LoginContext createLoginContext(/*<special_parameters>*/) {
        // ...
    }
}

In the unit test, we will use the createLoginContext(…) method and modify its output:

Tested tested = new Tested();
LoginContext loginContextWithoutJaas = Mockito.spy(tested.createLoginContext(...));
Mockito.doNothing().when(loginContextWithoutKerberos).login();

It remains to make a modified copy of Tested, where the createLoginContext() method returns the modified LoginContext:

Tested testedWithoutJaas = Mockito.spy(tested);
Mockito.when(testedWithoutJaas.createLoginContext()).thenReturn(loginContextWithoutJaas);

Next, you can use testedWithoutJaas instance in the unit test:

@Test 
public void xTest() {
    // ...
    // <preparing testedWithoutJaas instance>
    // ...
    String actual = testedWithoutJaas.x();
    String expected = "123";
    assertEquals(expected, actual);
}