Spocklight: Support for Hamcrest Matchers

Spock has support for Hamcrest matchers and adds some extra syntactic sugar. In an expect: block in a Spock specification method we can use the following syntax value Matcher. Let's create a sample Spock specification and use this syntax with the Hamcrest matcher hasKey:

// File: SampleSpecification.groovy
package com.mrhaki.spock

@Grab('org.hamcrest:hamcrest-all:1.3')
import static org.hamcrest.Matchers.*

@Grab('org.spockframework:spock-core:0.7-groovy-2.0')
import spock.lang.Specification

class SampleSpecification extends Specification {

    def "sample usage of hamcrest matcher hasKey"() {
        given:
        final sampleMap = [name: 'mrhaki']

        expect:
        sampleMap hasKey('name')
        sampleMap not(hasKey('name')) // To show assertion message.
    }

}

We can run the code ($groovy SampleSpecification.groovy) and see in the output a very useful assertion message for the second matcher in the expect: block. We directly see what went wrong and what was expected.

$ groovy SampleSpecification.groovy
JUnit 4 Runner, Tests: 1, Failures: 1, Time: 210
Test Failure: sample usage of hamcrest matcher hasKey(com.mrhaki.spock.SampleSpecification)
Condition not satisfied:

sampleMap not(hasKey('name'))
|         |
|         false
[name:mrhaki]

Expected: not map containing ["name"->ANYTHING]
     but: was <{name=mrhaki}>

 at com.mrhaki.spock.SampleSpecification.sample usage of hamcrest matcher hasKey(SampleSpecification.groovy:18)

With Spock we can rewrite the specification and use the static method that() in spock.util.matcher.HamcrestSupport as a shortcut for the Hamcrest assertThat() method. The following sample shows how we can use that(). With this method we can use the assertion outside an expect: or then: block.

// File: SampleSpecification.groovy
package com.mrhaki.spock

@Grab('org.hamcrest:hamcrest-all:1.3')
import static org.hamcrest.Matchers.*

@Grab('org.spockframework:spock-core:0.7-groovy-2.0')
import static spock.util.matcher.HamcrestSupport.*
import spock.lang.Specification

class SampleSpecification extends Specification {

    def "sample usage of hamcrest matcher hasKey"() {
        given:
        final sampleMap = [name: 'mrhaki']

        expect:
        that sampleMap, hasKey('name')
    }

}

Finally we can use the expect() method in spock.util.matcher.HamcrestSupport to add the assertion in a then: block. This improves readability of our specification.

// File: SampleSpecification.groovy
package com.mrhaki.spock

@Grab('org.hamcrest:hamcrest-all:1.3')
import static org.hamcrest.Matchers.*

@Grab('org.spockframework:spock-core:0.7-groovy-2.0')
import static spock.util.matcher.HamcrestSupport.*
import spock.lang.Specification

class SampleSpecification extends Specification {

    def "sample usage of hamcrest matcher hasKey"() {
        when:
        final sampleMap = [name: 'mrhaki']

        then:
        expect sampleMap, hasKey('name')
    }

}

Code written with Spock 0.7-groovy-2.0