Android Studio 2.1: error: package org.junit does not exist

I'm setting up unit testing on Android studio.

I have read the documentation and set it up exactly as specified. I have my test folder set up as src/test/java

I've made a random test class:

import org.junit.Test;
import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;

public class RandomTestClass
{
    @Test
    public void testTest()
    {
        assertThat(4, is(4));
    }
}

However when I go to run my test I get:

error: package org.junit does not exist

I've set up my gradle EXACTLY as descibed in the docs:

dependencies {
    // Required -- JUnit 4 framework
    testCompile 'junit:junit:4.12'
    // Optional -- Mockito framework
    testCompile 'org.mockito:mockito-core:1.10.19'
}

The few other questions with this issue seemed to say these dependencies are missing. I have them.

Can you think of any reason my Local Unit Tests are not finding the JUNIT file when I go to run the test?