JUnit assertThat: check that Object equals String

Question

I have Map declared as following:

Map<String, Object> data

I put a String in it and verify its value like this:

assertEquals("value", data.get("key"));

Now, I'd like to rewrite the verification to use assertThat instead of assertEquals. I've tried the following:

assertThat(data.get("key"), equalTo("value"));

And of course it didn't work because of type mismatch:

Wrong 2nd argument type. Found: 'org.hamcrest.Matcher<java.lang.String>', required: 'org.hamcrest.Matcher<? super java.lang.Object>' less...

Explicit type cast of the first argument to String helps, but I'd like to avoid it. For example assertEquals doesn't require type cast. So, how can I check that the value, which was put into Map object, declared above, is equal to particular String, using the assertThat method?

Answer 1

The "more assertThat" way of doing things would be:

Map<String, Object> expectedData = Collections.singletonMap("key", "value");

asssertThat(data, is(expectedData));

Please note:

• Maybe you need type hints for the call to singletonMap
• Besides the is matcher, there are other matchers that would allow you to check that data contains your "expected" map data

For your specific problem: that is caused because how generics come into play here; it might be sufficient to use (String) data.get("key") - to tell the compiler that the "actual" argument is of type String.

In the end - I have no idea what your problem is. I wrote down this piece of code:

public void test() {
    Map<String, Object> data = new HashMap<>();
    data.put("key", "value");
    assertThat(data.get("key"), is("value"));

    Map<String, Object> expectedData = Collections.singletonMap("key", "value");
    assertThat(data, is(expectedData));
}

It compiles fine, and the unit test runs and passes. In other words: actually I am unable to repro your problem.