How do I add a new sourceset to Gradle?

I want to add integration tests to my Gradle build (Version 1.0). They should run separately from my normal tests because they require a webapp to be deployed to localhost (they test that webapp). The tests should be able to use classes defined in my main source set. How do I make this happen?

Update for 2021:

A lot has changed in 8ish years. Gradle continues to be a great tool. Now there's a whole section in the docs dedicated to configuring Integration Tests. I recommend you read the docs now.

Original Answer:

This took me a while to figure out and the online resources weren't great. So I wanted to document my solution.

This is a simple gradle build script that has an intTest source set in addition to the main and test source sets:

apply plugin: "java"

sourceSets {
    // Note that just declaring this sourceset creates two configurations.
    intTest {
        java {
            compileClasspath += main.output
            runtimeClasspath += main.output
        }
    }
}

configurations {
    intTestCompile.extendsFrom testCompile
    intTestRuntime.extendsFrom testRuntime
}

task intTest(type:Test){
    description = "Run integration tests (located in src/intTest/...)."
    testClassesDir = project.sourceSets.intTest.output.classesDir
    classpath = project.sourceSets.intTest.runtimeClasspath
}