Testing against Kotlin at LightCodeInsightFixtureTestCase

Need to test highlighting at Kotlin files:

public class KdcrCodeInsightTest extends LightCodeInsightFixtureTestCase {

  public void testHighlighting() {
    doKotlinTest("fun foo(){ ");
    doJavaTest("class MyClass { ");
  }

  private long doKotlinTest(@NotNull String testingText) {
    myFixture.configureByText("myTmpFile.kt", testingText);
    return myFixture.checkHighlighting(false, true, false, false);
  }

  private long doJavaTest(@NotNull String testingText) {
    myFixture.configureByText("myTmpFile.java", testingText);
    return myFixture.checkHighlighting(false, true, false, false);
  }
}

doKotlinTest() passed and doJavaTest() fails (with <error descr="'}' expected"> </error> as expected).

Looks like testing environment doesn't have Kotlin support and treat any `.kt` file as just plain text.

Trying to add `kotlin-plugin.jar` as a library through overriding getProjectDescriptor() doesn't help either:

@Override
@NotNull
protected LightProjectDescriptor getProjectDescriptor() {
  return new DefaultLightProjectDescriptor(){
    @Override
    public void configureModule(@NotNull Module module, @NotNull ModifiableRootModel model, @NotNull ContentEntry contentEntry) {
      super.configureModule(module, model, contentEntry);
      PsiTestUtil.addLibrary(module, getBundledKotlinJarPath());
    }

    private String getBundledKotlinJarPath() {
      String jarPath = PathManager.getJarPathForClass(Kotlin.class);
      assert jarPath != null : "Cannot find JAR containing Kotlin classes";
      return jarPath;
    }
  };
}

When looking around through other plugins source: its seems that Kotlin support works out of the box for them or adding the syntax-supporting plugin as a library works (like for tests in Groovy plugin).

I feel like missing some stupidly-simple setup step... Any bits of advice are highly appreciating.