Gradle + Selenium is probably not a popular framework yet when I was developing it as I find it difficult to look for relevant resources online. There were bits and pieces of information here and there which I then glue then up together.

My build.gradle contains the following implementations:

(1) Add cucumberRuntime under Configurations

configurations {
cucumberRuntime {
extendsFrom testRuntime
}

}

(2) Source sets

sourceSets{
test{
groovy{
srcDirs ‘src/test’
}
}

}

(3) Compile test output

task testJar(type: Jar){
from(sourceSets.test.output){
include ‘**/*.class’
exclude ‘**/*StepDef*.class’
}

}

(4) Glue everything together

task cucumber() {
    dependsOn assemble, compileTestJava
    doLast {
        javaexec {
            main = "cucumber.api.cli.Main"
            classpath = configurations.cucumberRuntime + sourceSets.main.output + sourceSets.test.output
            args = ['-f', 'json:target/cucumber-report.json','--plugin','pretty', '--glue', 'src/test/groovy/au/com/story/steps', 'src/test/groovy/au/com/story/features']
        }
    }
}