groovy - Throw IOException in multiple return results with Spock -

i'm testing error handling. want first call mockedobject.foo() throw new ioexception, , second return bar. tried following code,

mockedobject.foo() >>> [{throw new ioexception()}, bar] 

but, when run test, error stating closure cannot cast bar,

foospec$_$spock_feature_0_1_closure2 cannot cast bar

how can mock behavior spock?

edit: after seeing documentation referenced tim_yates, changed test to,

mockedobject.foo() >>> firstbar >> {throw new ioexception()} >> secondbar 

this comes close enough testing needed test. following code threw same exception, i'm guessing spock setting return type of mocked method based on first object return.

mockedobject.foo() >>> {throw new ioexception()} >> secondbar 

here, complete working example:

@grab('org.spockframework:spock-core:0.7-groovy-2.0') @grab('cglib:cglib:3.1')  @grab('org.ow2.asm:asm-all:5.0.3')   import spock.lang.*  class mytestspec extends specification {        def 'spec'() {       given:       def = new a()       a.b = mock(b) {          foob() >> { throw new exception('aaa') } >> 1       }        when:       a.fooa()        then:       def e = thrown(exception)               e.message == 'aaa'        when:       def r = a.fooa()        then:       r == 1    } }  class {      b b = new b()      integer fooa() {         b.foob()     } }  class b {     integer foob() {         2     } }