WRITING CUSTOM HAMCREST MATCHERS

To make all matchers available in your file add an static import. The following is an example for defining a matcher which allows testing if a String matches a regular expression. See Wiki on Hamcrest for more details. This means that it will call the matchers many times during the test, maybe even after the expectation has already been matched and invoked. The following expectation specifies that the error method of the logger object must be called once with an argument that is a string starting with “FATAL”.

It does two things: The first generation used assert logical statement but such tests were not easily readable. In fact, jMock gives no guarantees of when and how many times it will call the matchers. 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. More documentation about how to write Matchers is available from the Hamcrest project 8. To create a new matcher:

Using Hamcrest matchers also provides more type safety as these matchers use generics. Even though the notANumber method creates a new matcher each time it is called, you should not assume this is the only usage pattern for your matcher.

This tutorial explains testing with the Hamcrest matcher framework. This commonly occurs when you find a fragment of code that tests the same set of properties over and over again and in different testsand you want to bundle the fragment into a single assertion.

In such cases, you can easily define new matchers that seamlessly extend the existing set defined by jMock. It is possible to write your custom Hamcrest matcher by extending TypeSafeMatcher.

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Hamcrest uses assertThat method with a matcher expression to determine if the test was succesful. The following is an example for defining a matcher which allows testing haamcrest a String matches a regular expression.

In this example, the ckstom of the assertion is the object biscuit that is the first method parameter. There are a number of situations where matchers are invaluble, such as UI validation, or data filtering, but it is in the area of writing flexible tests that matchers marchers most commonly used.

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We statically import this method to use the matcher in our test:. To make all matchers available in your file add an static import. Using Hamcrest collection matchers for arrays 4. List ; import static org. The constructor of FeatureMatcher takes the following arguments in this order: When dispatching 6 each invocation, jMock uses the matchers to find an expectation that matches the invocation’s arguments.

Hamcrest strives to make your tests as readable as possible. In contrast to BaseMatcher the TypeSafeMatcher class automatically checks for null values, checks the type and casts appropriately before delegating to matchesSafely. If Todo is constructed with the summary “Learn Hamcrest” that the summary property was initialized with this value.

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You can adjust this output in the describeMismatch method. Combining matchers Combining matchers is supported by Hamcrest out of the box but it has the limitation that the error is hard to read: Such tests fail when the behaviour of the aspect under test deviates from the expected behaviour, yet continue to pass when minor, unrelated changes to the behaviour are made.

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The assertThat method is a generic method which takes a Matcher parameterized by the mattchers of the subject of the assertion. RegexMatcher ; import org. The following snippets compare pure JUnit 4 assert statements with Hamcrest matchers.

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

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If you get the following exception “java. Matcher ; import org.

writing custom hamcrest matchers

The following expectation specifies that the error method of the logger object hamrcest be hamcrrst once with an argument that is a string starting with “FATAL”. Todo has a property called “summary” If Todo is constructed with the summary “Learn Hamcrest” that the summary property was initialized with this value Two objects created with the same values, have the same property values.

The last form is allowed since is T value is overloaded to return is equalTo value. Test ; import java.

jMock – Writing Custom Matchers

In fact, jMock gives no guarantees of when and how many times it will call the matchers. By grouping them into a single class you can import them with one statement.

Using Hamcrest String matchers 4. Arrays ; import java.

writing custom hamcrest matchers

Target Assume the following code: