Cajon - Concise AssertJ Optimizing Nitpicker

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

Purpose

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, when using the available special assertion methods of AssertJ, a failure of a condition can be expressed in better detail and with more meaningful descriptions. This makes finding bugs and fixing failed tests more efficient. Nobody likes to read failures of the kind "failed because true is not false".

For example:

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

If the collection has more or less than five 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 actual 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.

Lookup and refactoring of string-based extracting()

AssertJ allows extracting POJO fields/properties on iterables/arrays.

Using strings is not safe for refactoring (and before Java 8 Lambdas were available, creating extractor functions just for testing purpose was a bit too tedious).

This plugin adds support for referencing these fields (so you can ctrl(/cmd)-click on the string to go to the definition) and also allows safe refactoring on the fields (refactoring a getter method without a corresponding field will not work correctly right now).

Usage

The plugin will report inspections in your opened editor file as warnings. You can then quick-fix these with your quick-fix hotkey (usually Alt-Return or Opt-Return).

Or, you can use the "Run Inspection by Name..." action to run one inspection on a bigger scope (e.g. the whole project). Applying a quick fix might result in further optimization possibilities, so you might need to perform a couple of fixes before you get to the final result.

Check out this example where every line represents the result after a Cajon quickfix:

assertFalse(!(array.length == collection.size()));

assertThat(!(array.length == collection.size())).isFalse();

assertThat(array.length == collection.size()).isTrue();

assertThat(array.length).isEqualTo(collection.size());

assertThat(array).hasSameSizeAs(collection);

You can toggle the various inspections in the Settings/Editor/Inspections in the AssertJ group.

Implemented inspections

• AssertThatObjectIsNullOrNotNull

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

• AssertThatBooleanCondition

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

• AssertThatInvertedBooleanCondition

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

• AssertThatInstanceOf

  from: assertThat(object instanceof classname).isEqualTo(true);
  from: assertThat(object instanceof classname).isTrue();
    to: assertThat(object).isInstanceOf(classname.class);
  
  from: assertThat(object instanceof classname).isEqualTo(false);
  from: assertThat(object instanceof classname).isFalse();
    to: assertThat(object).isNotInstanceOf(classname.class);
  

• AssertThatStringIsEmpty

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

• AssertThatStringExpression

  from: assertThat(stringActual.isEmpty()).isTrue();
    to: assertThat(stringActual).isEmpty();
  
  from: assertThat(stringActual.equals(stringExpected)).isTrue();
  from: assertThat(stringActual.contentEquals(charSeqExpected)).isTrue();
    to: assertThat(stringActual).isEqualTo(stringExpected);
  
  from: assertThat(stringActual.equalsIgnoreCase(stringExpected)).isTrue();
    to: assertThat(stringActual).isEqualToIgnoringCase(stringExpected);
  
  from: assertThat(stringActual.contains(stringExpected)).isTrue();
    to: assertThat(stringActual).contains(stringExpected);
  
  from: assertThat(stringActual.startsWith(stringExpected)).isTrue();
    to: assertThat(stringActual).startsWith(stringExpected);
  
  from: assertThat(stringActual.endsWith(stringExpected)).isTrue();
    to: assertThat(stringActual).endsWith(stringExpected);
  

  Analogously with isFalse().

• 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);
  

  and additionally with AssertJ 13.2.0 or later

  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, strings and CharSequences, e.g:

  from: assertThat("string".length()).isLessThan(1);
    to: assertThat("string").isEmpty();
  
  from: assertThat("string".length()).isEqualTo(collection.size())
    to: assertThat("string").hasSameSizeAs(collection);
  

• AssertThatBinaryExpression

  from: assertThat(primActual == primExpected).isTrue();
    to: assertThat(primActual).isEqualTo(primExpected);
  
  from: assertThat(10 < primActual).isNotEqualTo(false);
    to: assertThat(primActual).isGreaterThan(primExpected);
  
  from: assertThat(objActual != objExpected).isEqualTo(true);
    to: assertThat(objActual).isNotSameAs(objExpected);
  
  from: assertThat(null == objActual).isFalse();
    to: assertThat(objActual).isNotNull();
  
  from: assertThat(objActual.equals(objExpected).isTrue();
    to: assertThat(objActual).isEqualTo(objExpected);
  

  ...and many, many more combinations (more than 150).

• AssertThatJava8Optional

  from: assertThat(opt.isPresent()).isEqualTo(true);
  from: assertThat(opt.isPresent()).isNotEqualTo(false);
  from: assertThat(opt.isPresent()).isTrue();
    to: assertThat(opt).isPresent();
  
  from: assertThat(opt.isPresent()).isEqualTo(false);
  from: assertThat(opt.isPresent()).isNotEqualTo(true);
  from: assertThat(opt.isPresent()).isFalse();
    to: assertThat(opt).isNotPresent();
  
  from: assertThat(opt.get()).isEqualTo("foo");
    to: assertThat(opt).contains("foo");
  
  from: assertThat(opt.get()).isSameAs("foo");
    to: assertThat(opt).containsSame("foo"); 
  
  from: assertThat(opt).isEqualTo(Optional.of("foo"));
  from: assertThat(opt).isEqualTo(Optional.ofNullable("foo"));
    to: assertThat(opt).contains("foo"); 
  
  from: assertThat(opt).isEqualTo(Optional.empty());
    to: assertThat(opt).isNotPresent();
  
  from: assertThat(opt).isNotEqualTo(Optional.empty());
    to: assertThat(opt).isPresent();
  

• AssertThatGuavaOptional

  from: assertThat(opt.isPresent()).isEqualTo(true);
  from: assertThat(opt.isPresent()).isNotEqualTo(false);
  from: assertThat(opt.isPresent()).isTrue();
    to: assertThat(opt).isPresent();
  
  from: assertThat(opt.isPresent()).isEqualTo(false);
  from: assertThat(opt.isPresent()).isNotEqualTo(true);
  from: assertThat(opt.isPresent()).isFalse();
    to: assertThat(opt).isAbsent();
  
  from: assertThat(opt.get()).isEqualTo("foo");
    to: assertThat(opt).contains("foo");
  
  from: assertThat(opt).isEqualTo(Optional.of("foo"));
  from: assertThat(opt).isEqualTo(Optional.fromNullable("foo"));
    to: assertThat(opt).contains("foo"); 
  
  from: assertThat(opt).isEqualTo(Optional.absent());
    to: assertThat(opt).isAbsent();
  
  from: assertThat(opt).isNotEqualTo(Optional.absent());
    to: assertThat(opt).isPresent();
  

  AssertJ for Guava needs to be available in the classpath.

• 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);
  

Implemented referencing

.extracting("field")
.extracting("outerField.fieldInsideObjectTypeOfOuterField.andSoOn")
.extracting("property") // where the class has a getProperty() (or isProperty() for boolean) method
.extracting("bareMethod") // supported with AssertJ 13.12.0
.extracting(Extractors.byName("fieldOrPropertyOrBareMethod")
.extracting(Extractors.byName("fieldOrPropertyOrBareMethod.orAPathLikeAbove")
.extracting(Extractors.resultOf("bareMethod")
.extractingResultOf("bareMethod")
.flatExtracting("fieldOrPropertyOrBareMethod.orAPathLikeAbove")
.flatExtracting(Extractors.byName("fieldOrPropertyOrBareMethod.orAPathLikeAbove")
.flatExtracting(Extractors.resultOf("bareMethod")

Works on both POJOs and Iterables/Arrays. Implementation is very basic though and does not work with fancy cascaded .extracting() sequences. If there's demand, I will add it.

Development notice

Cajon is written in Kotlin 1.3.

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 it 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

• AssumeThatInsteadOfReturn

• Join consecutive assertThats

• 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())...
  

• Kotlin support (right now, however, with less than 100 downloads after a month, this is unlikely to happen)

Changelog

V0.6 (22-Apr-19)

• New AssertThatStringExpression inspection that will move isEmpty(), equals(), equalsIgnoreCase(), contains(), startsWith(), and endsWith() out of actual expression.
• Extended AssertThatSize inspection to take Strings and CharSequences into account, too.
• New AssertThatInvertedBooleanCondition inspection that will remove inverted boolean expressions inside assertThat().
• Renamed a few inspections to better/shorter names.
• New AssertThatInstanceOf inspection that moves instanceof expressions out of assertThat().

V0.5 (18-Apr-19)

• Fixed incompatibility with IDEA versions < 2018.2 (affected AssertThatSizeInspection). Minimal version is now 2017.3.
• Fixed missing Guava imports (if not already present) for AssertThatGuavaInspection. This was a major PITA to get right.
• Added support for referencing and refactoring inside .extracting() methods with fields, properties and methods (though getter renaming does not work that perfect, but I'm giving up for now as the IntelliJ SDK docs are seriously lacking).
• Fixed an exception in batch mode if the description string was the same but for different fixes. Now descriptions are different for quick fixes triggered by AssertThatJava8OptionalInspection and AssertThatGuavaOptionalInspection.

V0.4 (11-Apr-19)

• Reduced minimal supported IDEA version from 2018.2 to 2017.2.
• New inspection AssertThatJava8Optional that operates on Java 8 Optional objects and tries to use contains(), containsSame(), isPresent(), and isNotPresent() instead.
• New inspection AssertThatGuavaOptional that operates on Guava Optional objects and tries to use contains(), isPresent(), and isAbsent() instead.
• Added support in AssertThatBinaryExpressionIsTrueOrFalse for is(Not)EqualTo(Boolean.TRUE/FALSE).

V0.3 (07-Apr-19)

• New inspection AssertThatBinaryExpressionIsTrueOrFalse that will find and fix common binary expressions and equals() statements (more than 150 combinations) inside assertThat().
• Merged AssertThatObjectIsNull and AssertThatObjectIsNotNull to AssertThatObjectIsNullOrNotNull.
• Support for hasSizeLessThan(), hasSizeLessThanOrEqualTo(), hasSizeGreaterThanOrEqualTo(), and hasSizeGreaterThan() for AssertThatSizeInspection (with AssertJ >=13.2.0).
• Really fixed highlighting for JUnit conversion. Sorry.

V0.2 (01-Apr-19)

• Fixed descriptions and quick fix texts.
• Fixed highlighting of found problems and also 'Run inspection by Name' returning nothing.

V0.1 (31-Mar-19)

• Initial release.