Gradle: How to get output from test STDERR/STDOUT into console?

Add these lines to build.gradle :

apply plugin: 'java'

test {
    dependsOn cleanTest
    testLogging.showStandardStreams = true
}

Notice: dependsOn cleanTest is not necessary but if not used, you need to run cleanTest or clean task before test task.

---

Edit:

A better approach:

apply plugin: 'java'

test {
    testLogging {
        outputs.upToDateWhen {false}
        showStandardStreams = true
    }
}

Notice: outputs.upToDateWhen {false} is not necessary but if not used, you need to run cleanTest or clean task before test task.

For more info and options see the documentation.

For those using Kotlin/Kotlin DSL for Gradle, you need to put the following in your build.gradle.kts file:

tasks.withType<Test> {
    this.testLogging {
        this.showStandardStreams = true
    }
}

Also as mentioned in another answer, you will need to run gradle clean test for the output to print every time.