custom error message for assertThat() in junit?

Question

I was wondering if assertThat() has a way of adding a custom error message ?

for example in this :

assertThat(file.exists(), is(equalTo(true)));

I would like to add some custom message, saying which file name doesnt exist

Answer 1

I would prefer the following, to avoid the reader believing that you wish to assert that the file name doesn't exist..!

assertThat("File name should exist", file.exists(), is(equalTo(true)));

Answer 2

Use the overloaded assertThat method

assertThat("File name doesn't exist", file.exists(), is(equalTo(true)));

Answer 3

I prefer this, since one can read it as a sentence: "assert that file 'myFile' exist: myFile exists is true"

assertThat("File '" + myFile + "' exists", myFile.exists(), is(true));

And one gets also readable message with all necessary information when it fails:

java.lang.AssertionError: File '/blah' exists
Expected: is <true>
     but: was <false>

Answer 4

You may want to simply use the assertTrue() methods with 2 args:

Assert.assertTrue("File "+file.getAbsoluePath()+"does not exist", file.exists());

Answer 5

I use this method :

Throwable thrown = catchThrowable(() -> myTestedObject.funtion());
assertThat("Error Message", thrown, isInstanceOf(MyException.class));