Common utilities for working with JUnit:

• assertion of exceptions, as well as exception details, such as message and cause
• assertion of strings contents
• testing that a class cannot be instantiated

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Examples

Note: Consider the following static import declarations for readability:

import static net.obvj.junit.utils.matchers.AdvancedMatchers.*;
import static org.hamcrest.CoreMatchers.*;
import static org.hamcrest.MatcherAssert.assertThat;

Asserting exceptions

The following assertion is true if the examined method throws a NullPointerException:

assertThat(() -> myObject.doStuff(null),
        throwsException(NullPointerException.class));

To test the exception message, add withMessageContaining ...

assertThat(() -> myObject.doStuff(null),
        throwsException(NullPointerException.class)
            .withMessageContaining("ERR-120008"));

... or combine a String matcher:

assertThat(() -> agent.loadSchemaFile("bad-schema.xsd"),
        throwsException(AgentConfigurationException.class)
            .withMessage(
                either(startsWith("ERR-0001"))
                    .or(containsAny("invalid schema").ignoreCase())));

If required, you can also test the exception cause:

assertThat(() -> myObject.doStuff(null),
        throwsException(MyException.class).withMessageContaining("ERR-120008")
            .withCause(NullPointerException.class));

Including cause details:

assertThat(() -> myObject.doStuff(null),
        throwsException(MyException.class).withMessageContaining("ERR-120008")
            .withCause(
                exception(NullPointerException.class)
                    .withMessage("stuff cannot be null")));

And more:

assertThat(() -> httpClient.post(request),
        throwsException(HttpException.class)
            .with(HttpException::getStatusCode, equalTo(400));

Testing that instantiation is not allowed

The following assertion is particularly useful for utility classes:

assertThat(TestUtils.class, instantiationNotAllowed());

A matching class shall have all constructors declared as private and throw an exception inside the default constructor.

Testing the contents of a string

The following examples represent some successful assertions using the Advanced String matcher:

assertThat("The quick brown fox jumps over the lazy dog", containsAll("dog", "fox"));
assertThat("The quick brown fox jumps over the lazy dog", containsAny("FOX", "dragon").ignoreCase());
assertThat("The quick brown fox jumps over the lazy dog", containsNone("centaur"));
assertThat("The quick brown fox jumps over the lazy dog", containsAllInSequence("fox", "dog"));

Testing numbers

Sometimes, it's more meaningful to check whether a number is positive or negative than testing the value itself, especially in situations where the exact value is unpredictable:

assertThat(stopwatch.elapsedTime(),           isPositive());
assertThat(duration.compareTo(otherDuration), isNegative());

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How to include it

If you are using Maven, add junit-utils as a dependency in your pom.xml file:

<dependency>
    <groupId>net.obvj</groupId>
    <artifactId>junit-utils</artifactId>
    <version>1.9.0</version>
</dependency>

If you use other dependency management systems (such as Gradle, Grape, Ivy, etc.) click here.