Maven is great and mature. There is always a solution on almost everything. The main case you might stumble on organisation projects is dependency management. Instead of each project having it’s own dependencies you want a centralised way to inherit those dependencies.

In those case you declare on the parent prom the managed dependencies. In my example I just want to include the Akka stream dependencies.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>org.example</groupId>
	<artifactId>maven-dependency-management</artifactId>
	<packaging>pom</packaging>
	<version>1.0-SNAPSHOT</version>

	<properties>
		<akka.version>2.5.31</akka.version>
		<akka.http.version>10.1.11</akka.http.version>
		<scala.binary.version>2.12</scala.binary.version>
	</properties>

	<modules>
		<module>child-one</module>
	</modules>


	<dependencyManagement>
		<dependencies>
			<dependency>
				<groupId>com.typesafe.akka</groupId>
				<artifactId>akka-stream_2.12</artifactId>
				<version>${akka.version}</version>
			</dependency>
			<dependency>
				<groupId>com.typesafe.akka</groupId>
				<artifactId>akka-http_2.12</artifactId>
				<version>${akka.http.version}</version>
			</dependency>
			<dependency>
				<groupId>com.typesafe.akka</groupId>
				<artifactId>akka-http-spray-json_2.12</artifactId>
				<version>${akka.http.version}</version>
			</dependency>
		</dependencies>
	</dependencyManagement>

</project>

What I use is the dependency management block.

Now the child project would be able to include those libraries without specifying the version. Having the version derived and managed is essential. Many unpleasant surprises can come if a version is incompatible.

Now on to the child module the versions are declared without the version since it is the child module.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<parent>
		<artifactId>maven-dependency-management</artifactId>
		<groupId>org.example</groupId>
		<version>1.0-SNAPSHOT</version>
	</parent>
	<modelVersion>4.0.0</modelVersion>

	<artifactId>child-one</artifactId>

	<dependencies>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-stream_2.12</artifactId>
		</dependency>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-http_2.12</artifactId>
		</dependency>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-http-spray-json_2.12</artifactId>
		</dependency>
	</dependencies>

</project>

On another note sometimes we want to use another project’s dependency management without that project being our parent. Those are cases where you need to include the dependency management from a parent project when you already have a parent project.

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

	<modelVersion>4.0.0</modelVersion>

	<groupId>org.example</groupId>
	<artifactId>independent-project</artifactId>
	<version>1.0-SNAPSHOT</version>

	<dependencyManagement>
		<dependencies>
			<dependency>
				<artifactId>maven-dependency-management</artifactId>
				<groupId>org.example</groupId>
				<version>1.0-SNAPSHOT</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

	<dependencies>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-stream_2.12</artifactId>
		</dependency>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-http_2.12</artifactId>
		</dependency>
		<dependency>
			<groupId>com.typesafe.akka</groupId>
			<artifactId>akka-http-spray-json_2.12</artifactId>
		</dependency>
	</dependencies>
</project>

As you can see in the block

	<dependencyManagement>
		<dependencies>
			<dependency>
				<artifactId>maven-dependency-management</artifactId>
				<groupId>org.example</groupId>
				<version>1.0-SNAPSHOT</version>
				<type>pom</type>
				<scope>import</scope>
			</dependency>
		</dependencies>
	</dependencyManagement>

We included the dependency management from another project, which can be applied to inherit dependencies from multiple projects.

Implementing unit tests with maven is something ordinary and most of us are familiar with the project structure and where the unit tests reside.

However Integration tests are a different case and most of times they have pretty different requirements.
For example it is ok to have your unit tests operate on a h2 in memory database but when it comes to integration tests and complex queries, it is best for them to be executed against an actual relational database like the one used in production.

Considering the above example, chances are that our integration tests might have different configurations and dependencies.

So our goals for our integration tests is to keep them separate from other tests and to execute them separately.

Regarding our maven structure within the source directory we have the main ‘folder’ and test ‘folder’.

In the same fashion we will add an extra directory called ‘it’.
The ‘it’ directory will contain a java directory for our java sources and a resources directory. Same structure with the test directory.

Then we should give instruction to maven on building our code and adding it to our test sources.

                <plugin>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>build-helper-maven-plugin</artifactId>
                    <version>1.5</version>
                    <executions>
                        <execution>
                            <id>add-test-source</id>
                            <phase>process-resources</phase>
                            <goals>
                                <goal>add-test-source</goal>
                            </goals>
                            <configuration>
                                <sources>
                                    <source>src/it/java</source>
                                </sources>
                            </configuration>
                        </execution>
                    </executions>
                </plugin>

By using the build helper maven plugin we can instruct maven to add extra test source directories to our our build.

The next step is to instruct maven to run our unit tests. To do so we will use the maven failsafe plugin.

The Failsafe Plugin is designed to run integration tests while the Surefire Plugin is designed to run unit tests. The name (failsafe) was chosen both because it is a synonym of surefire and because it implies that when it fails, it does so in a safe way.

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-failsafe-plugin</artifactId>
                <version>2.15</version>
                <executions>
                    <execution>
                        <id>integration-test</id>
                        <goals>
                            <goal>integration-test</goal>
                        </goals>
                    </execution>
                    <execution>
                        <id>verify</id>
                        <goals>
                            <goal>verify</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>

Then to execute the integration tests we should issue.

mvn verify

As expected our integration tests run separately.

To sum up, we want to have integration tests separated from our unit tests. Also we want them to run separately. This can be achieved by utilizing the maven failsafe plugin.
You can find an example project on github.