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?

Yes, it helps. The point is that I want to avoid explicit type cast. Looking for a way to make it work like assertEquals but with assertThat. — Lingviston
– Lingviston, Commented Oct 10, 2016 at 10:44

GhostCat · Accepted Answer · 2016-10-10 11:09:36Z

6

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.

edited Oct 10, 2016 at 11:09

answered Oct 10, 2016 at 10:38

GhostCat

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5 Comments

Lingviston Over a year ago

Unfortunately "is" has the same issue as "equalsTo". It looks like I can't achieve what I want without explicit type cast to String.

GhostCat Over a year ago

Please see my updated answer. Things work for me (both ways) without any casting (but to be precise: using Java8). In Java7, type inference might give you a problem; requiring you to put down that cast.

Lingviston Over a year ago

Hmm, checked again exactly your example and experienced the same issue as before. So it definitely looks like version mismatch of anything. I'll continue researching and checking.

GhostCat Over a year ago

Lets be precise about wording: there is no "version" mismatch. What I am saying is: my code works fine with Java8. When you are using an older version from Java, the type inference works less good; therefore older Java might only work with hardcoded casts.

Lingviston Over a year ago

Yes, that what I meant. Sorry, if it confused you. At least your comment shows that the desired approach is working.

Ali Hasan · Accepted Answer · 2019-05-06 19:20:54Z

3

try this

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

or

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

edited May 6, 2019 at 19:20

answered May 6, 2019 at 18:38

Ali Hasan

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1 Comment

Miroslav Glamuzina Over a year ago

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