We'll continue where we left off with Tic-Tac-Toe in Chapter 3, Red-Green-Refactor: From Failure Through Success until Perfection. The complete source code of the application developed so far can be found at https://bitbucket.org/vfarcic/tdd-java-ch06-tic-tac-toe-mongo.git. Use the VCS | Checkout from Version Control | Git option from the IntelliJ IDEA to clone the code. As with any other project, the first thing we need to do is add the dependencies to build.gradle:

dependencies {
    compile 'org.jongo:jongo:1.1'
    compile 'org.mongodb:mongo-java-driver:2.+'
    testCompile 'junit:junit:4.11'
    testCompile 'org.mockito:mockito-all:1.+'
}

Importing the MongoDB driver should be self-explanatory. Jongo is a very helpful set of utility methods that make working with Java code in a way much more similar to the Mongo query language. For the testing part, we'll continue using JUnit with an addition of Mockito mocks, spies, and validations.

You'll notice that we won...