@RunWith(JUnitParamsRunner.class)
@RunWith(XtextRunner)
class MyDslValidationTest {
   // test code ... 
}

import com.google.inject.Inject
import junitparams.JUnitParamsRunner
import junitparams.Parameters
import org.eclipse.xtext.formatting.INodeModelFormatter
import org.eclipse.xtext.formatting.impl.DefaultNodeModelFormatter
import org.eclipse.xtext.junit4.util.ParseHelper
import org.eclipse.xtext.resource.XtextResource
import org.eclipse.xtext.util.Pair
import org.eclipse.xtext.util.Tuples
import org.junit.Before
import org.junit.Test
import org.junit.runner.RunWith

import static extension org.assertj.core.api.Assertions.*

@RunWith(JUnitParamsRunner)
class TestFormatterTest {

	@Inject extension ParseHelper<Model> parseHelper = new ParseHelper
	@Inject extension INodeModelFormatter nodeModelFormatter = new DefaultNodeModelFormatter

	@Before
	def void before() {
		var i = new TestStandaloneSetup().createInjectorAndDoEMFRegistration
		i.injectMembers(parseHelper)
		i.injectMembers(nodeModelFormatter)
	}

	@Test
	@Parameters
	def void testFormat(Pair<CharSequence, CharSequence> pair) {
		pair.first.assertFormattedAs(pair.second)
	}

	def static parametersForTestFormat() {
		#[
			Tuples.create('''test { bla }''',
					'''test {
                                                bla
                                               }''')
		]
	}

	def void assertFormattedAs(CharSequence input, CharSequence expected) {
		(input.parse.eResource as XtextResource).parseResult.rootNode.format(0, input.length).formattedText.assertThat.
			isEqualTo(expected)
	}
}