When running a test with Gradle and trying to print to System.out or System.err nothing happens. How to make Gradle to display standard output?

Here’s sample Gradle buildscript:

buildscript {
    repositories {
        mavenCentral()
    }
}

apply plugin: 'java'
apply plugin: 'groovy'

repositories {
    mavenCentral()
}

dependencies {
    compile "org.codehaus.groovy:groovy-all:2.4.1"
    testCompile "org.spockframework:spock-core:1.0-groovy-2.4"
}

And here’s a sample test class that prints to standard output:

package com.farenda.solved

import spock.lang.Specification

class StandardOutPrintTest extends Specification {

    def 'should tell nothing but the true'() {
        println('Inside the test!')
        expect:
        42 == 42
    }
}

Now, when you run the test from the console, you will see that it prints nothing:

$> gradle test --tests com.farenda.solved.StandardOutPrintTest
:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:compileTestJava UP-TO-DATE
:compileTestGroovy UP-TO-DATE
:processTestResources UP-TO-DATE
:testClasses UP-TO-DATE
:test UP-TO-DATE

BUILD SUCCESSFUL

Total time: 7.158 secs

The problem is that Gradle is not logging messages printed to standard out/err, so you have to tell it to do that in your buildscript, using the following command:

buildscript {
    repositories {
        mavenCentral()
    }
}

apply plugin: 'java'
apply plugin: 'groovy'

repositories {
    mavenCentral()
}

// this turns logging on in tests:
test.testLogging.showStandardStreams = true

dependencies {
    compile "org.codehaus.groovy:groovy-all:2.4.1"
    testCompile "org.spockframework:spock-core:1.0-groovy-2.4"
}

Now, when you rerun the test it will print standard out/err as expected:

$> gradle cleanTest test --tests com.farenda.solved.StandardOutPrintTest
:cleanTest
:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:compileTestJava UP-TO-DATE
:compileTestGroovy UP-TO-DATE
:processTestResources UP-TO-DATE
:testClasses UP-TO-DATE
:test

com.farenda.solved.StandardOutPrintTest > should tell nothing but the true STANDARD_OUT
    Inside the test!

BUILD SUCCESSFUL

Total time: 8.684 secs

It works as advertised! :-) As you can see, I had to rerun the test with cleanTest task to make Gradle to actually run the test. It is because when Gradle sees that nothing has changed it does nothing.