void () { PsiClass aClass = myFixture.addClass("class Foo {double foo(double d) {return d;}}"); List<String> suggestedTypes = ContainerUtil.map(FunctionalInterfaceSuggester.suggestFunctionalInterfaces(aClass.getMethods()[0]), PsiType::getCanonicalText); assertEquals(4, suggestedTypes.size()); assertTrue(suggestedTypes.containsAll(Arrays.asList("java.util.function.ToDoubleFunction<java.lang.Double>", "java.util.function.Function<java.lang.Double,java.lang.Double>", "java.util.function.DoubleUnaryOperator", "java.util.function.DoubleFunction<java.lang.Double>"))); }