Why doesn't JUnit provide assertNotEquals methods?

I'd suggest you use the newer assertThat() style asserts, which can easily describe all kinds of negations and automatically build a description of what you expected and what you got if the assertion fails:

assertThat(objectUnderTest, is(not(someOtherObject)));
assertThat(objectUnderTest, not(someOtherObject));
assertThat(objectUnderTest, not(equalTo(someOtherObject)));

All three options are equivalent, choose the one you find most readable.

To use the simple names of the methods (and allow this tense syntax to work), you need these imports:

import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;

There is an assertNotEquals in JUnit 4.11: https://github.com/junit-team/junit/blob/master/doc/ReleaseNotes4.11.md#improvements-to-assert-and-assume

import static org.junit.Assert.assertNotEquals;

I wonder same. The API of Assert is not very symmetric; for testing whether objects are the same, it provides assertSame and assertNotSame.

Of course, it is not too long to write:

assertFalse(foo.equals(bar));

With such an assertion, the only informative part of the output is unfortunately the name of the test method, so descriptive message should be formed separately:

String msg = "Expected <" + foo + "> to be unequal to <" + bar +">";
assertFalse(msg, foo.equals(bar));

That is of course so tedious, that it is better to roll your own assertNotEqual. Luckily in future it will maybe be part of the JUnit: JUnit issue 22