[Hamcrest] Using Hamcrest for testing

Using Hamcrest for testing - Tutorial

1. Purpose of the Hamcrest matcher framework

Hamcrest is a framework for software tests. Hamcrest allows checking for conditions in your code via existing matchers classes. It also allows you to define your custom matcher implementations.

Hamcrest는 소프트웨어 테스트를위한 framework입니다. Hamcrest는 기존 matchers 클래스를 통해 코드의 조건을 확인할 수 있습니다. 또한 사용자 정의 matcher implementations 을 정의 할 수 있습니다.

To use Hamcrest matchers in JUnit you use the assertThat statement followed by one or several matchers.

JUnit에서 Hamcrest matcher를 사용하려면 assertThat 문 뒤에 하나 또는 여러 개의 matchers를 사용합니다.

Hamcrest is typically viewed as a third generation matcher framework. The first generation used assert(logical statement) but such tests were not easily readable. The second generation introduced special methods for assertions, e.g., assertEquals(). This approach leads to lots of assert methods. Hamcrest uses assertThat method with a matcher expression to determine if the test was succesful. See Wiki on Hamcrest for more details.

Hamcrest는 일반적으로 3 세대 정규식 framework로 간주됩니다. 1 세대는 assert(logical statement)을 사용했지만 그러한 테스트는 쉽게 읽을 수 없었습니다. 2 세대에서는 assertEquals()와 같은 assertions을 위한 특수한 메소드가 도입되었습니다. 이 접근법은 많은 assert methods 를 필요로 합니다. Hamcrest는 assertThat 메서드를 사용하여 테스트가 성공적인지 여부를 확인하는 matcher expression을 사용합니다. 자세한 내용은 Hamcrest의 Wiki를 참조하십시오.

Hamcrest has the target to make tests as readable as possible. For example, the is method is a thin wrapper for equalTo(value).

Hamcrest는 최대한 가독성있는 test scripts를 가지는 것을 목표로 하고 있습니다. 예를 들어, is 메소드는 equalTo(value)에 대한 thin wrapper입니다.

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.equalTo;

boolean a;
boolean b;

// all statements test the same
assertThat(a, equalTo(b));
assertThat(a, is(equalTo(b)));
assertThat(a, is(b));

The following snippets compare pure JUnit 4 assert statements with Hamcrest matchers.

다음 snippets은 순수 JUnit 4 assert statements와 Hamcrest matchers를 비교합니다.

// JUnit 4 for equals check
assertEquals(expected, actual);
// Hamcrest for equals check
assertThat(actual, is(equalTo(expected)));

// JUnit 4 for not equals check
assertNotEquals(expected, actual)
// Hamcrest for not equals check
assertThat(actual, is(not(equalTo(expected))));

It is also possible to chain matchers, via the anyOf of allOf method.

allOf 메소드의 anyOf를 통해 matcher를 연결할 수도 있습니다.

assertThat("test", anyOf(is("testing"), containsString("est")));

In general the Hamcrest error messages are also much easier to read.

일반적으로 Hamcrest 오류 메시지는 읽기가 훨씬 쉽습니다.

assertTrue(result instanceof String);
// error message:
java.lang.AssertionError
    at org.junit.Assert.fail(Assert.java:86)
    at org.junit.Assert.assertTrue(Assert.java:41)
    at org.junit.Assert.assertTrue(Assert.java:52)
// ...


assertEquals(String.class, result.getClass());
// error message:
java.lang.NullPointerException
    at com.vogella.hamcrest.HamcrestTest.test(HamcrestTest.java:30)
// ....


assertThat(result, instanceOf(String.class));
// error message:
java.lang.AssertionError:
Expected: an instance of java.lang.String
     but: null
    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:8)
// ...

Using Hamcrest matchers also provides more type safety as these matchers use generics.

Hamcrest matchers를 사용하면 matcher가 generics를 사용하므로 더 많은 type safety을 제공합니다.

2. Using Hamcrest matchers

2.1. Defining a Hamcrest dependency for Gradle

To use Hamcrest matchers for a project based on the Gradle build system, add the following dependencies to it.

Gradle 빌드 시스템을 기반으로하는 프로젝트에 Hamcrest matchers를 사용하려면 다음 dependencies를 추가하십시오.

dependencies {
    // Unit testing dependencies
    testCompile 'junit:junit:4.12'
    // Set this dependency if you want to use Hamcrest matching
    testCompile 'org.hamcrest:hamcrest-library:1.3'
}

2.2. Defining a Hamcrest dependency for Maven

To use the library for a Maven based project, the following dependency to your pom file.

Maven 기반 프로젝트에 라이브러리를 사용하려면, pom 파일에 다음과 같은 dependencies를 부여하십시오.

<dependency>
<groupId>org.hamcrest</groupId>
<artifactId>hamcrest-library</artifactId>
<version>1.3</version>
<scope>test</scope>
</dependency>

2.3. Adding Hamcrest directly to the classpath in Eclipse

The JUnit distribution included in Eclipse only contain the core Hamcrest matcher. To use all available matchers, download the latest hamcrest-all-*.jar from https://code.google.com/p/hamcrest/downloads/list and add it to your projects classpath.

Eclipse에 포함 된 JUnit 배포판에는 core Hamcrest matcher 만 포함됩니다. 사용 가능한 모든 matcher를 사용하려면 https://code.google.com/p/hamcrest/downloads/list에서 최신 hamcrest-all - * .jar 파일을 다운로드하여 프로젝트 classpath에 추가하십시오.

If you get the following exception "java.lang.SecurityException: class "org.hamcrest.Matchers"'s signer information does not match signer information of other classes in the same package", ensure that the hamcrest jar is before the Junit library in the build path. You an configure the order in the project properties in the Eclipse IDE under Java Build Path on the Order and Export tab.

"java.lang.SecurityException : class"org.hamcrest.Matchers "의 서명자 정보가 같은 패키지의 다른 클래스의 서명자 정보와 일치하지 않는 경우"hamcrest jar가 Junit 라이브러리보다 앞에 있는지 확인하십시오. 빌드 경로. Eclipse IDE의 프로젝트 특성에서 순서 및 내보내기 탭의 Java 빌드 경로 아래에 순서를 구성하십시오.

3. Using Hamcrest

3.1. Example

The usage of Hamcrest matchers is demonstrates by the following code snippet.

Hamcrest matchers의 사용법은 다음 code snippet을 통해 보여줍니다.

assertThat(Long.valueOf(1), instanceOf(Integer.class));
// shortcut for instanceOf
assertThat(Long.valueOf(1), isA(Integer.class));

3.2. Static import

To make all matchers available in your file add an static import. This also makes it easier to find matchers through code completion.

파일에서 모든 matcher를 사용할 수 있게 하려면 static import를 추가하십시오. 이러면 code completion을 통해 matcher를 쉽게 찾을 수 있도록 해 주기도 합니다.

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.*;

3.3. Hamcrest matchers for lists

The usage of the Hamcrest matchers for lists are demonstrated by the following example.

lists에 대한 Hamcrest matchers의 사용법은 다음 예제에서 보여 줍니다.

import org.junit.Test;

import java.util.Arrays;
import java.util.List;

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.contains;
import static org.hamcrest.Matchers.containsInAnyOrder;
import static org.hamcrest.Matchers.greaterThan;
import static org.hamcrest.collection.IsCollectionWithSize.hasSize;
import static org.hamcrest.core.Every.everyItem;

public class HamcrestListMatcherExamples {
    @Test
    public void listShouldInitiallyBeEmpty() {
        List<Integer> list = Arrays.asList(5, 2, 4);

        assertThat(list, hasSize(3));

        // ensure the order is correct
        assertThat(list, contains(5, 2, 4));

        assertThat(list, containsInAnyOrder(2, 4, 5));

        assertThat(list, everyItem(greaterThan(1)));

    }
}

// Check that a list of objects has a property race and
// that the value is not ORC
assertThat(fellowship, everyItem(hasProperty("race", is(not((ORC))))));

3.4. Overview of Hamcrest mather

The following are the most important Hamcrest matchers:

다음은 가장 중요한 Hamcrest matchers들 입니다.

• allOf - matches if all matchers match (short circuits)

• anyOf - matches if any matchers match (short circuits)

• not - matches if the wrapped matcher doesn’t match and vice

• equalTo - test object equality using the equals method

• is - decorator for equalTo to improve readability

• hasToString - test Object.toString

• instanceOf, isCompatibleType - test type

• notNullValue, nullValue - test for null

• sameInstance - test object identity

• hasEntry, hasKey, hasValue - test a map contains an entry, key or value

• hasItem, hasItems - test a collection contains elements

• hasItemInArray - test an array contains an element

• closeTo - test floating point values are close to a given value

• greaterThan, greaterThanOrEqualTo, lessThan, lessThanOrEqualTo

• equalToIgnoringCase - test string equality ignoring case

• equalToIgnoringWhiteSpace - test string equality ignoring differences in runs of whitespace

• containsString, endsWith, startsWith - test string matching

To see all matchers, use API reference.

모든 matchers를 보려면 API 참조를 사용하십시오.

4. Exercise - Writing a custom Hamcrest matcher using FeatureMatcher

4.1. Target

The target of this exercise is to write a custom matcher with Hamcrest.

이 exercise의 목표는 Hamcrest 에서 custom matcher를 작성하는 것입니다.

4.2. Create Hamcrest Matchers

Define a custom matcher for Hamcrest which provides the length matcher for a String. We want to use the class FeatureMatcher. With FeatureMatcher we can wrap an existing Matcher, decide which field of the given Object under test to match and provide a nice error message. The constructor of FeatureMatcher takes the following arguments in this order:

Hamcrest를위한 custom matcher를 정의하여 String에 대한 length matcher를 제공합니다. 우리는 FeatureMatcher 클래스를 사용하고자합니다. FeatureMatcher를 사용하면 기존 Matcher를 wrap하고 테스트 할 대상 객체의 필드를 결정하여 나은 오류 메시지를 제공 할 수 있습니다. FeatureMatcher의 생성자는 다음 순서로 인수를 취합니다.

• The matcher we want to wrap

• a description of the feature that we tested

• a description of the possible mismatch

The only method we have to overwrite is featureValueOf(T actual) which returns the value which will get passed into the wrapped matches()/matchesSafely() method.

overwrite하는 유일한 방법은 wrapped matches () / matchesSafely () 메서드에 전달 될 값을 반환하는 featureValueOf (T actual)입니다.

public static Matcher<String> length(Matcher<? super Integer> matcher) {
    return new FeatureMatcher<String, Integer>(matcher, "a String of length that", "length") {
        @Override
        protected Integer featureValueOf(String actual) {
            return actual.length();
        }
    };
}

4.3. Validate

Use your custom matcher to check that "Gandalf" has a lenght of 8.

Gandalf의 길이가 8인지에 대해 여러분의 custom matcher 를 사용해서 확인해 보세요.

@Test
public void fellowShipOfTheRingShouldContainer7() {
        assertThat("Gandalf", length(is(8)));
}
public static  Matcher<String> length(Matcher<? super Integer> matcher) {
        return new FeatureMatcher<String, Integer>(matcher, "a String of length that", "length") {
                @Override
                protected Integer featureValueOf(String actual) {
                  return actual.length();
                }
        };
}

5. Exercise: Writing your custom Hamcrest matcher using TypeSafeMatcher

It is possible to write your custom Hamcrest matcher by extending TypeSafeMatcher. In contrast to BaseMatcher the TypeSafeMatcher class automatically checks for null values, checks the type and casts appropriately before delegating to matchesSafely(). It provides type safety by default. The following is an example for defining a matcher which allows testing if a String matches a regular expression.

TypeSafeMatcher를 extends하여 custom Hamcrest matcher를 작성할 수 있습니다. BaseMatcher와 달리 TypeSafeMatcher 클래스는 자동으로 null 값을 확인하고, types를 검사하고 matchesSafely ()에 위임하기 전에 적절하게 형 변환합니다. 기본적으로 type safety 을 제공합니다. 다음은 문자열이 정규 표현식 regular expression 과 일치하는지 테스트 할 수있는 matcher를 정의하는 예제입니다.

import org.hamcrest.Description;
import org.hamcrest.TypeSafeMatcher;

public class RegexMatcher extends TypeSafeMatcher<String> {

        private final String regex;

        public RegexMatcher(final String regex) {
                this.regex = regex;
        }

        @Override
        public void describeTo(final Description description) {
                description.appendText("matches regular expression=`" + regex + "`");
        }

        @Override
        public boolean matchesSafely(final String string) {
                return string.matches(regex);
        }


         // matcher method you can call on this matcher class
    public static RegexMatcher matchesRegex(final String regex) {
        return new RegexMatcher(regex);
    }
}

The following snippet gives an example how to use it.

다음 snippet에는 이를 사용하는 예가 나와 있습니다.

package com.vogella.android.testing.applicationtest;


import org.junit.Test;

import static org.hamcrest.MatcherAssert.assertThat;

public class TestCustomMatcher {

    @Test
    public void testRegularExpressionMatcher() throws Exception {
        String s ="aaabbbaaaa";
        assertThat(s, RegexMatcher.matchesRegex("a*b*a*"));
    }

}

6. Exercise: Combining matchers

Combining matchers is supported by Hamcrest out of the box but it has the limitation that the error is hard to read:

matchers를 결합하는 것은 Hamcrest에 오류가 읽기 어렵다는 제한이 있습니다.

@Test
public void () {
    List<Integer> list = new ArrayList<>();
    assertThat(list, both(hasSize(1)).and(contains(42)));
}

Expected: (a collection with size <1> and iterable containing [<42>])
     but: a collection with size <1> collection size was <0>.

This not very readable.

이렇게 가독성이 떨어집니다.

6.1. Target

We want to write our own MatcherCombiner that provides us with a readable error message, even when multiple matchers fail.

우리는 multiple matchers가 fail하더라도 가독성있는 에러 메시지를 제공하는 MatcherCombiner를 별도로 작성하려고합니다.

6.2. Create MatchCombiner

We do this by inheriting from BaseMatch and by providing a starting method that let’s us chain matchers together. The matchers get saved in a list that we iterate over during the matching phase.

우리는 BaseMatch로부터 상속하고 chain matcher를 함께 묶어주는 것을 시작하면서 이 작업을 수행합니다. matchers는 matching phase 동안에 반복되는 list 저장됩니다.

public class MatcherCombinator<T> extends BaseMatcher<T> {
    private final List<Matcher<? super T>> matchers = new ArrayList<>();
    private final List<Matcher<? super T>> failedMatchers = new ArrayList<>();

    private MatcherCombinator(final Matcher<? super T> matcher) {
        matchers.add(matcher);
    }

    public MatcherCombinator<T> and(final Matcher<? super T> matcher) {
        matchers.add(matcher);
        return this;
    }

    @Override
    public boolean matches(final Object item) {
        boolean matchesAllMatchers = true;
        for (final Matcher<? super T> matcher : matchers) {
            if (!matcher.matches(item)) {
                failedMatchers.add(matcher);
                matchesAllMatchers = false;
            }
        }
        return matchesAllMatchers;
    }

    @Override
    public void describeTo(final Description description) {
        description.appendValueList("\n", " " + "and" + "\n", "", matchers);
    }

    @Override
    public void describeMismatch(final Object item, final Description description) {
        description.appendText("\n");
        for (Iterator<Matcher<? super T>> iterator = failedMatchers.iterator(); iterator.hasNext();) {
            final Matcher<? super T> matcher = iterator.next();
            description.appendText("Expected: <");
            description.appendDescriptionOf(matcher).appendText(" but ");
            matcher.describeMismatch(item, description);
            if (iterator.hasNext()) {
                description.appendText(">\n");
            }
        }
    }

    public static <LHS> MatcherCombinator<LHS> matches(final Matcher<? super LHS> matcher) {
        return new MatcherCombinator<LHS>(matcher);
    }
}

To validate the implementation we write a new test.

implementation을 validate하기 위해 새로운 테스트를 작성합니다.

@Test
public void test() {
    List<Integer> list = new ArrayList<>();
    assertThat(list, matches(hasSize(1)).and(contains(42)));
}

java.lang.AssertionError:
Expected:
<a collection with size <1>> and
<iterable containing [<42>]>
     but:
Expected: <a collection with size <1> but collection size was <0>>
Expected: <iterable containing [<42>] but No item matched: <42>.

You can adjust this output in the describeMismatch method.

describeMismatch method 에서 이 output을 adjust 할 수 있습니다.

7. Grouping your matchers for import

If you define many custom matchers it might become tedious to import them one by one into your test files. By grouping them into a single class you can import them with one statement. You can also group them together with Hamcrest matchers.

많은 custom matchers를 정의하면 테스트 파일에 하나씩 import하는 것이 불편 할 수 있습니다. single class로 그룹화하여 하나의 statement로 가져올 수 있습니다. Hamcrest matchers와 함께 그룹화 할 수도 있습니다.

package com.vogella.hamcrest;
import com.vogella.hamcrest.matchers.RegexMatcher;
import org.hamcrest.Matcher;
import org.hamcrest.Matchers;

public class MyMatchers
{
    public static <T> Matcher<T> instanceOf(Class<T> target) {
        return Matchers.instanceOf(target);
    }

   public static Matcher<String> matchesRegex(String target) {
          return RegexMatcher.matchesRegex(target);
   }
}

In your test file:

import static com.vogella.hamcrest.MyMatchers.*;

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