Java Coding Problems

178. Testing methods that use lambdas

Let's start by testing a lambda that is not wrapped in a method. For example, the following lambda is associated with a field (for being reused), and we want to test its logic:

public static final Function<String, String> firstAndLastChar  = (String s) -> String.valueOf(s.charAt(0))    + String.valueOf(s.charAt(s.length() - 1));

Let's take into account that a lambda generates an instance of a functional interface; then, we can test the behavior of that instance as follows:

@Testpublic void testFirstAndLastChar() throws Exception {  String text = "Lambda";  String result = firstAndLastChar.apply(text);  assertEquals("La", result);}

Another solution consists of wrapping the lambda in a method call and writing ...