Mock static method with GroovyMock or similar in Spock

Here is how I solved my similar issue (mocking a static method call which is being called from another static class) with Spock (v1.0) and PowerMock (v1.6.4)

import org.junit.Rule
import org.powermock.core.classloader.annotations.PowerMockIgnore
import org.powermock.core.classloader.annotations.PrepareForTest
import org.powermock.modules.junit4.rule.PowerMockRule
import spock.lang.Specification
import static org.powermock.api.mockito.PowerMockito.mockStatic
import static org.powermock.api.mockito.PowerMockito.when

@PrepareForTest([YourStaticClass.class])
@PowerMockIgnore(["javax.xml.*", "ch.qos.logback.*", "org.slf4j.*"])
class YourSpockSpec extends Specification {

@Rule
Powermocked powermocked = new Powermocked();

def "something something something something"() {
    mockStatic(YourStaticClass.class)

    when: 'something something'
    def mocked = Mock(YourClass)
    mocked.someMethod(_) >> "return me"

    when(YourStaticClass.someStaticMethod(xyz)).thenReturn(mocked)

    then: 'expect something'
    YourStaticClass.someStaticMethod(xyz).someMethod(abc) == "return me"

   }
}

The @PowerMockIgnore annotation is optional, only use it if there is some conflicts with existing libraries

Spock can only mock static methods implemented in Groovy. For mocking static methods implemented in Java, you'll need to use a tool like GroovyMock , PowerMock or JMockit.

PS: Given that these tools pull of some deep tricks in order to achieve their goals, I'd be interested to hear if and how well they work together with tests implemented in Groovy/Spock (rather than Java/JUnit).