[Java Test Tip] Assertj 로 좀 더 직관적인 테스트설계를 하자!

AssertJ란? 

java test를 위해 좀 더 풍부한 문법을 제공하고 메서드 체이닝을 통해 직관적인 테스트 흐름을 작성할 수 있도록 개발된 오픈소스 라이브러리이다. 최근 junit에 필수로 사용되고 있는 추세이다.

공식홈페이지

http://joel-costigliola.github.io/assertj/

maven

<dependency>
   <groupId>org.assertj</groupId>
   <artifactId>assertj-core</artifactId>
   <!-- use 2.8.0 for Java 7 projects -->
   <version>3.8.0</version>
   <scope>test</scope>
</dependency>

gradle

testCompile 'org.assertj:assertj-core:3.8.0'

실사용예 - 공식홈페이지에서 발췌.

    // entry point for all assertThat methods and utility methods (e.g. entry)
import static org.assertj.core.api.Assertions.*;

    // basic assertions
    assertThat(frodo.getName()).isEqualTo("Frodo");
    assertThat(frodo).isNotEqualTo(sauron);

    // chaining string specific assertions
    assertThat(frodo.getName()).startsWith("Fro")
                           .endsWith("do")
                           .isEqualToIgnoringCase("frodo");

    // collection specific assertions (there are plenty more)
    // in the examples below fellowshipOfTheRing is a List<TolkienCharacter>
    assertThat(fellowshipOfTheRing).hasSize(9)
                               .contains(frodo, sam)
                               .doesNotContain(sauron);

    // as() is used to describe the test and will be shown before the error message
    assertThat(frodo.getAge()).as("check %s's age", frodo.getName()).isEqualTo(33);

    // Java 8 exception assertion, standard style ...
    assertThatThrownBy(() -> { throw new Exception("boom!"); }).hasMessage("boom!");
    // ... or BDD style
    Throwable thrown = catchThrowable(() -> { throw new Exception("boom!"); });
    assertThat(thrown).hasMessageContaining("boom");

    // using the 'extracting' feature to check fellowshipOfTheRing character's names (Java 7)
    assertThat(fellowshipOfTheRing).extracting("name")
                               .contains("Boromir", "Gandalf", "Frodo", "Legolas")
    // same thing using a Java 8 method reference
    assertThat(fellowshipOfTheRing).extracting(TolkienCharacter::getName)
                               .doesNotContain("Sauron", "Elrond");

    // extracting multiple values at once grouped in tuples (Java 7)
    assertThat(fellowshipOfTheRing).extracting("name", "age", "race.name")
                               .contains(tuple("Boromir", 37, "Man"),
    tuple("Sam", 38, "Hobbit"),
    tuple("Legolas", 1000, "Elf"));

    // filtering a collection before asserting in Java 7 ... 
    assertThat(fellowshipOfTheRing).filteredOn("race", HOBBIT)
                               .containsOnly(sam, frodo, pippin, merry);
    // ... or in Java 8
    assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o"))
        .containsOnly(aragorn, frodo, legolas, boromir);

    // combining filtering and extraction (yes we can)
    assertThat(fellowshipOfTheRing).filteredOn(character -> character.getName().contains("o"))
        .containsOnly(aragorn, frodo, legolas, boromir)
                               .extracting(character -> character.getRace().getName())
        .contains("Hobbit", "Elf", "Man");

    // and many more assertions : iterable, stream, array, map, dates (java 7 and java 8), path, file, numbers, predicate, optional ...