Grails Unit Testing: Mocking With MetaClass Stubs

On a recent project I ran into issues with testing controllers in Grails. Starting test first, I spent some early time figuring out how much support there was out of the box for unit testing Grails domain classes and controllers. I setup Spock as a plugin and plunged in. I was dealing with a legacy database which had 100% compound primary keys so many of the findBy type operations that are well supported for controller testing are of no help. Often I found I needed to mock a call to a find or findAll with HQL syntax or a criteria call. I knew metaClass mocking could work here, but I wanted to understand better how that would impact the rest of the code after I started replacing methods on the fly. Turns out Grails unit testing has built in support for cleaning up metaClass hacking after every test with the registerMetaClass() method in GrailsUnitTestCase. Mrhaki has a good post on this. Here’s an Spock example:

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import grails.plugin.spock.ControllerSpec


class ContractControllerSpec extends ControllerSpec {

  def setup() {
    registerMetaClass Contract
  }

 def "validateContract() returns true for an existing contract"() {
    given:
    mockDomain(Contract)
    def contract = new Contract(division: '33', unit: '99', contractNumber: 'C7777777').save(flush: true)
    controller.params.division = '33'
    controller.params.unit = '99'
    controller.params.contractNumber = 'C7777777'
    Contract.metaClass.static.find = { String query, Map namedArgs -> contract }

    when:
    controller.validateContract()

    then:
    "TRUE" == controller.response.contentAsString
  }

}

Grails has support for the same idea using mockFor(), but the syntax is much like EasyMock. The same test would look like:

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import grails.plugin.spock.ControllerSpec


class ContractControllerSpec extends ControllerSpec {

 def "validateContract() returns true for an existing contract"() {
    given:
    mockDomain(Contract)
    def contract = new Contract(division: '33', unit: '99', contractNumber: 'C7777777').save(flush: true)
    controller.params.division = '33'
    controller.params.unit = '99'
    controller.params.contractNumber = 'C7777777'

  // EasyMock like syntax
  def mockContract = mockFor(Contract)
    mockContract.demand.static.find(..5) { String query, Map namedArgs -> null }

    when:
    controller.validateContract()

    then:
    "TRUE" == controller.response.contentAsString
  }

}

For pure stubs I prefer the syntax of just using MetaClass. I often don’t care about validating the exact calls to the dependent class so I don’t really want a full mock. You don’t need a call to registerMetaClass() because mockFor() does this for you.