(Quick Reference) # 15.1.2 Unit Testing Tag Libraries Version: 3.2.8 ## 15.1.2 Unit Testing Tag Libraries #### The Basics Tag libraries and GSP pages can be tested with the `grails.test.mixin.web.GroovyPageUnitTestMixin` mixin. To use the mixin declare which tag library is under test with the `TestFor` annotation:
    import grails.test.mixin.TestFor
    import spock.lang.Specification

    @TestFor(SimpleTagLib)
    class SimpleTagLibSpec extends Specification {

        void "test something"() {
        }
    }
Adding the `TestFor` annotation to a TagLib class causes a new `tagLib` field to be automatically created for the TagLib class under test. The tagLib field can be used to test calling tags as function calls. The return value of a function call is either a StreamCharBuffer instance or the object returned from the tag closure when returnObjectForTags feature is used. Note that if you are testing invocation of a custom tag from a controller you can combine the `ControllerUnitTestMixin` and the `GroovyPageUnitTestMixin` using the `Mock` annotation:
    import grails.test.mixin.TestFor
    import grails.test.mixin.Mock
    import spock.lang.Specification

    @TestFor(SimpleController)
    @Mock(SimpleTagLib)
    class SimpleControllerSpec extends Specification {

    }
#### Testing Custom Tags The core Grails tags don’t need to be enabled during testing, however custom tag libraries do. The `GroovyPageUnitTestMixin` class provides a `mockTagLib()` method that you can use to mock a custom tag library. For example consider the following tag library:
    class SimpleTagLib {

        static namespace = 's'

        def hello = { attrs, body ->
            out << "Hello ${attrs.name ?: 'World'}"
        }

        def bye = { attrs, body ->
            out << "Bye ${attrs.author.name ?: 'World'}"
        }
    }
You can test this tag library by using `TestFor` and supplying the name of the tag library:
    import grails.test.mixin.TestFor
    import spock.lang.Specification

    @TestFor(SimpleTagLib)
    class SimpleTagLibSpec extends Specification {

        void "test hello tag"() {
            expect:
            applyTemplate('<s:hello />') == 'Hello World'
            applyTemplate('<s:hello name="Fred" />') == 'Hello Fred'
            applyTemplate('<s:bye author="${author}" />', [author: new Author(name: 'Fred')]) == 'Bye Fred'
        }

        void "test tag calls"() {
            expect:
            tagLib.hello().toString() == 'Hello World'
            tagLib.hello(name: 'Fred').toString() == 'Hello Fred'
            tagLib.bye(author: new Author(name: 'Fred')).toString == 'Bye Fred'
        }
    }
Alternatively, you can use the `TestMixin` annotation and mock multiple tag libraries using the `mockTagLib()` method:
    import spock.lang.Specification
    import grails.test.mixin.TestMixin
    import grails.test.mixin.web.GroovyPageUnitTestMixin

    @TestMixin(GroovyPageUnitTestMixin)
    class MultipleTagLibSpec extends Specification {

        void "test multiple tags"() {
            given:
            mockTagLib(SomeTagLib)
            mockTagLib(SomeOtherTagLib)

            expect:
            // ...
        }
    }
The `GroovyPageUnitTestMixin` provides convenience methods for asserting that the template output equals or matches an expected value.
    import grails.test.mixin.TestFor
    import spock.lang.Specification

    @TestFor(SimpleTagLib)
    class SimpleTagLibSpec extends Specification {

        void "test hello tag"() {
            expect:
            assertOutputEquals ('Hello World', '<s:hello />')
            assertOutputMatches (/.*Fred.*/, '<s:hello name="Fred" />')
        }
    }
#### Testing View and Template Rendering You can test rendering of views and templates in `grails-app/views` via the `render(Map)` method provided by `GroovyPageUnitTestMixin` :
    import spock.lang.Specification
    import grails.test.mixin.TestMixin
    import grails.test.mixin.web.GroovyPageUnitTestMixin

    @TestMixin(GroovyPageUnitTestMixin)
    class RenderingSpec extends Specification {

        void "test rendering template"() {
            when:
            def result = render(template: '/simple/hello')

            then:
            result == 'Hello World!'
        }
    }
This will attempt to render a template found at the location `grails-app/views/simple/_hello.gsp`. Note that if the template depends on any custom tag libraries you need to call `mockTagLib` as described in the previous section. Some core tags use the active controller and action as input. In GroovyPageUnitTestMixin tests, you can manually set the active controller and action name by setting controllerName and actionName properties on the webRequest object:
    webRequest.controllerName = 'simple'
        webRequest.actionName = 'hello'
| Quick Reference (hide)