Gradle Goodness: Show Standard Out or Error Output from Tests

We use the Test task in Gradle to run tests. If we use the System.out.println or System.err.println methods in our test we don't see the output when we execute the tests. We can customize the test task to show any output send to standard out or error in the Gradle output.

First we show our test class written with Spock, but it could also be a JUnit or TestNG test:

view sourceprint?
00.// File: src/test/groovy/com/mrhaki/gradle/SampleSpec.groovy
01.package com.mrhaki.gradle
02. 
03.import spock.lang.*
04. 
05.class SampleSpec extends Specification {
06. 
07.def "check that Gradle is Gr8"() {
08.when:
09.def value = 'Gradle is great!'
10. 
11.then:
12.// Include a println statement, so
13.// we have output to show.
14.println "Value = [$value]"
15.value == 'Gradle is great!'
16.}
17. 
18.}

Now we write a simple Gradle build file which can execute our test:

view sourceprint?
0.// File: build.gradle
1.apply plugin: 'groovy' // Adds test task
2. 
3.repositories.jcenter()
4. 
5.dependencies {
6.compile 'org.codehaus.groovy:groovy-all:2.3.7'
7.testCompile 'org.spockframework:spock-core:0.7-groovy-2.0'
8.}

Let's run the test task from the command line and look at the output:

$ gradle test
:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:compileTestJava
:compileTestGroovy
:processTestResources UP-TO-DATE
:testClasses
:test
 
BUILD SUCCESSFUL
 
Total time: 7.022 secs
$

Well at least our test is successful, but we don't see the output of our println method invocation in the test. We customize the test task and add the testLogging method with a configuration closure. In the closure we set the property showStandardStreams to the value true. Alternatively we can set the events property or use the events method with the values standard_out and standard_err to achieve the same result. In the next build file we use the showStandardStreams property:

view sourceprint?
00.// File: build.gradle
01.apply plugin: 'groovy' // Adds test task
02. 
03.repositories.jcenter()
04. 
05.dependencies {
06.compile 'org.codehaus.groovy:groovy-all:2.3.7'
07.testCompile 'org.spockframework:spock-core:0.7-groovy-2.0'
08.}
09. 
10.test {
11.testLogging {
12.// Make sure output from
13.// standard out or error is shown
14.// in Gradle output.
15.showStandardStreams = true
16. 
17.// Or we use events method:
18.// events 'standard_out', 'standard_error'
19. 
20.// Or set property events:
21.// events = ['standard_out', 'standard_error']
22. 
23.// Instead of string values we can
24.// use enum values:
25.// events org.gradle.api.tasks.testing.logging.TestLogEvent.STANDARD_OUT,
26.//        org.gradle.api.tasks.testing.logging.TestLogEvent.STANDARD_ERROR,
27.}
28.}

We re-run the test task from the command line and look at the output to see the result from the println method:

$ gradle test
:compileJava UP-TO-DATE
:compileGroovy UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:compileTestJava
:compileTestGroovy
:processTestResources UP-TO-DATE
:testClasses
:test
 
com.mrhaki.gradle.SampleSpec > check that Gradle is Gr8 STANDARD_OUT
Value = [Gradle is great!]
 
BUILD SUCCESSFUL
 
Total time: 8.716 secs
$

Written with Gradle 2.1.