Cajon - Concise AssertJ Optimizing Nitpicker

Cajon is an IntelliJ IDEA Plugin for shortening and optimizing AssertJ assertions.

Why?

First, code is easier to read, when it is concise and reflects the intention clearly. AssertJ has plenty of different convenience methods that describing various intentions precisely. Why write longer, more complex code that can be expressed in brevity?

Second, AssertJ is able to output more meaningful descriptions when an assertion fails. This makes finding bugs and fixing failed tests more efficient.

For example:

assertThat(collection.size()).isEqualTo(5);

If the collection has more or less than 5 elements, the assertion will fail, but will not tell you about the contents, making it hard to guess what went wrong.

Instead, if you wrote the same assertion the following way:

assertThat(collection).hasSize(5);

Then AssertJ would tell you the contents of the collection on failure.

Conversion of JUnit assertions to AssertJ

The plugin also supports the conversion of the most common JUnit 4 assertions to AssertJ.

Implemented inspections

• AssertThatObjectIsNullOrNotNull

  from: assertThat(object).isEqualTo(null);
    to: assertThat(object).isNull();
  
  from: assertThat(object).isNotEqualTo(null);  
    to: assertThat(object).isNotNull();
  

• AssertThatBooleanIsTrueOrFalse

  from: assertThat(booleanValue).isEqualTo(true/false/Boolean.TRUE/Boolean.FALSE);  
    to: assertThat(booleanValue).isTrue()/isFalse();
  

• AssertThatStringIsEmpty

  from: assertThat(charSequence/string).isEqualTo("");
  from: assertThat(charSequence/string).hasSize(0);
    to: assertThat(charSequence/string).isEmpty();
  

• AssertThatEnumerableIsEmpty

  from: assertThat(enumerable).hasSize(0);
    to: assertThat(enumerable).isEmpty();
  

• AssertThatSize

  from: assertThat(array.length).isEqualTo(0);
  from: assertThat(array.length).isLessThanOrEqualTo(0);
  from: assertThat(array.length).isLessThan(1);
  from: assertThat(array.length).isZero();
    to: assertThat(array).isEmpty();
  
  from: assertThat(array.length).isGreaterThan(0);
  from: assertThat(array.length).isGreaterThanOrEqualTo(1);
  from: assertThat(array.length).isNotZero();
    to: assertThat(array).isNotEmpty();
  
  from: assertThat(array.length).isEqualTo(anotherArray.length);
    to: assertThat(array).hasSameSizeAs(anotherArray);
  

  with AssertJ 13.2.0 or higher

  from: assertThat(array.length).isLessThanOrEqualTo(expression);
    to: assertThat(array).hasSizeLessThanOrEqualTo(expression);
  
  from: assertThat(array.length).isLessThan(expression);
    to: assertThat(array).hasSizeLessThan(expression);
  
  from: assertThat(array.length).isGreaterThan(expression);
    to: assertThat(array).hasSizeGreaterThan(expression);
  
  from: assertThat(array.length).isGreaterThanOrEqualTo(expression);
    to: assertThat(array).hasSizeGreaterThanOrEqualTo(expression);
  

  and analogously for collections...

• JUnitAssertToAssertJ

  assertTrue(condition);
  assertTrue(message, condition);
  assertFalse(condition);
  assertFalse(message, condition);
  assertNull(object);
  assertNull(message, object);
  assertNonNull(object);
  assertNonNull(message, object);
  assertEquals(expected, actual);
  assertEquals(message, expected, actual);
  assertEquals(expectedDoubleOrFloat, actualDoubleOrFloat, delta);
  assertEquals(message, expectedDoubleOrFloat, actualDoubleOrFloat, delta);
  assertNotEquals(unexpected, actual);
  assertNotEquals(message, unexpected, actual);
  assertNotEquals(unexpectedDoubleOrFloat, actualDoubleOrFloat, delta);
  assertNotEquals(message, unexpectedDoubleOrFloat, actualDoubleOrFloat, delta);
  assertSame(expected, actual);
  assertSame(message, expected, actual);
  assertNotSame(unexpected, actual);
  assertNotSame(message, unexpected, actual);
  assertArrayEquals(expected, actual);
  assertArrayEquals(message, expectedArray, actualArray);
  assertArrayEquals(expectedDoubleOrFloatArray, actualDoubleOrFloatArray, delta);
  assertArrayEquals(message, expectedDoubleOrFloatArray, actualDoubleOrFloatArray, delta);
  

Development notice

Cajon is probably the only plugin that uses JUnit 5 Jupiter for unit testing so far (or at least the only one that I'm aware of ;) ). The IntelliJ framework actually uses the JUnit 3 TestCase for plugin testing and I took me quite a while to make it work with JUnit 5. Feel free to use the code (in package de.platon42.intellij.jupiter) for your projects (with attribution).

TODO

• AssertThatBinaryExpressionIsTrueOrFalse

  from: assertThat(actual == expected).isTrue();
    to: assertThat(actual).isEqualTo(expected); (for primitive types)
    to: assertThat(actual).isSameAs(expected); (for objects)
  
  from: assertThat(actual != expected).isFalse();
    to: assertThat(actual).isNotEqualTo(expected); (for primitive types)
    to: assertThat(actual).isNotSameAs(expected); (for objects)
  

• AssertThatJava8OptionalContains

  from: assertThat(Optional.of("foo").get()).isEqualTo("foo");
    to: assertThat(Optional.of("foo")).contains("foo");
  

• AssertThatJava8OptionalIsPresentOrAbsent

  from: assertThat(Optional.of("foo").isPresent()).isEqualTo(true);
  from: assertThat(!Optional.of("foo").isPresent()).isEqualTo(false);
  from: assertThat(Optional.of("foo").isPresent()).isTrue();
  from: assertThat(!Optional.of("foo").isPresent()).isFalse();
    to: assertThat(Optional.of("foo")).isPresent();
  
  from: assertThat(Optional.of("foo").isPresent()).isEqualTo(false);
  from: assertThat(!Optional.of("foo").isPresent()).isEqualTo(true);
  from: assertThat(Optional.of("foo").isPresent()).isFalse();
  from: assertThat(!Optional.of("foo").isPresent()).isTrue();
    to: assertThat(Optional.of("foo")).isNotPresent();
  

• AssertThatGuavaOptionalContains

  from: assertThat(Optional.of("foo").get()).isEqualTo("foo");
    to: assertThat(Optional.of("foo")).contains("foo");
  

• AssertThatGuavaOptionalIsPresentOrAbsent

  from: assertThat(Optional.of("foo").isPresent()).isEqualTo(true);
  from: assertThat(!Optional.of("foo").isPresent()).isEqualTo(false);
  from: assertThat(Optional.of("foo").isPresent()).isTrue();
  from: assertThat(!Optional.of("foo").isPresent()).isFalse();
    to: assertThat(Optional.of("foo")).isPresent();
  
  from: assertThat(Optional.of("foo").isPresent()).isEqualTo(false);
  from: assertThat(!Optional.of("foo").isPresent()).isEqualTo(true);
  from: assertThat(Optional.of("foo").isPresent()).isFalse();
  from: assertThat(!Optional.of("foo").isPresent()).isTrue();
    to: assertThat(Optional.of("foo")).isAbsent();
  

• Referencing string properties inside extracting()
• Extraction with property names to lambda with Java 8

  from: assertThat(object).extracting("propOne", "propNoGetter", "propTwo.innerProp")...
    to: assertThat(object).extracting(type::getPropOne, it -> it.propNoGetter, it -> it.getPropTwo().getInnerProp())...