This is a collection of stuff I implemented for Xtend (currently 2.8.4) and find useful to share with myself and others. Ideas for enhancements or different approaches are more than welcome, just create a ticket or send me a pull request.

io.franzbecker.xtend.junit This package provides utilities for unit testing.

In Xtend it is possible to use extension methods that allow us to "add" new methods to existing types without modifying them. In testing this becomes quite handy since we can "add" the assertion methods to the types we want to test.

Instead of writing: assertEquals(expected, actual) we could think about writing actual.assertEquals(expected).

Using this pattern assertions become much more readable than JUnit's default assertions and simple ones become slightly more readable than using truth or assertj. The methods of AssertionHelper were designed to allow chaining, but unlike pure-Java we don't need verbose fluent APIs as we can simply pass objects to a lambda using the with-operator.

Here are some sample assertions that you can do:

  // simple assertions
  val x = "x"
  val y = "y"
  x.assertEquals("x")
  x.assertNotEquals(y)
  x.assertSame(x)
  x.assertNotSame(y)
	
  // instance of assertion
  obj.assertInstanceOf(String).length.assertEquals(4)
  
  // assertions on iterable
  #[].assertEmpty
  #["test"].assertSingleElement => [
	assertEquals("test")
  ]

  // assertions on lambdas
  val divide = [BigDecimal x, BigDecimal y | x.divide(y)]
  
  [divide.apply(1bd, 0bd)].assertFail(ArithmeticException) => [
     message.assertEquals("Division by zero")
]

To implement the last example in AssertJ with Java 8 you would write:

	final BiFunction<BigDecimal, BigDecimal, BigDecimal> divide = (BigDecimal x, BigDecimal y) -> x.divide(y);
		
	assertThatThrownBy(() -> divide.apply(BigDecimal.ONE, BigDecimal.ZERO))
		.isInstanceOf(ArithmeticException.class)
		.hasMessage("Division by zero");

Note that the methods of AssertionHelper are non-static. This feels kind of strange but is has one major advantage which I found superior: we can declare it as an extension provider in a super class of all our tests. This way we don't need to add a static import everytime we create a new test class and also could exchange the implementation in the future.

io.franzbecker.xtend.lib This package provides utilities for the standard Java library.

Xtend already comes with a great default for extension methods. This package contains some more extensions that can be included on demand.