In Maven, you can declare the JUnit dependency like this:

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

But, it comes with a bundled copy of hamcrest-core library.

$ mvn dependency:tree
...
[INFO] \- junit:junit:jar:4.12:test
[INFO]    \- org.hamcrest:hamcrest-core:jar:1.3:test
...

1. Maven + JUnit + Hamcrest

Review the updated pom.xml again, it excludes the JUnit bundled copy of hamcrest-core. On the other hand, it also includes the useful hamcrest-library :

	<dependencies>
		<dependency>
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>4.12</version>
			<scope>test</scope>
			<exclusions>
				<exclusion>
					<groupId>org.hamcrest</groupId>
					<artifactId>hamcrest-core</artifactId>
				</exclusion>
			</exclusions>
		</dependency>
		<!-- This will get hamcrest-core automatically -->
		<dependency>
			<groupId>org.hamcrest</groupId>
			<artifactId>hamcrest-library</artifactId>
			<version>1.3</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

Review the dependency tree again.

$ mvn dependency:tree
...
[INFO] +- junit:junit:jar:4.12:test
[INFO] \- org.hamcrest:hamcrest-library:jar:1.3:test
[INFO]    \- org.hamcrest:hamcrest-core:jar:1.3:test
...

References

1. How to create a Java project with Maven
2. Maven – Display project dependency
3. JUnit – Use with Maven