One nice feature of the Spring Boot test integration is that it can allocate a free port for the web application. When the start goal of the plugin is used, the Spring Boot application is started separately, making it difficult to pass the actual port to the integration test itself.

The example below showcases how you could achieve the same feature using the build-helper-plugin:

<project>
  ...
  <build>
    ...
    <plugins>
      ...
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>build-helper-maven-plugin</artifactId>
        <executions>
          <execution>
            <id>reserve-tomcat-port</id>
            <goals>
              <goal>reserve-network-port</goal>
            </goals>
            <phase>process-resources</phase>
            <configuration>
              <portNames>
                <portName>tomcat.http.port</portName>
              </portNames>
            </configuration>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <version>2.1.0.RELEASE</version>
        <executions>
          <execution>
            <id>pre-integration-test</id>
            <goals>
              <goal>start</goal>
            </goals>
            <configuration>
              <arguments>
                <argument>--server.port=${tomcat.http.port}</argument>
              </arguments>
            </configuration>
          </execution>
          <execution>
            <id>post-integration-test</id>
            <goals>
              <goal>stop</goal>
            </goals>
          </execution>
        </executions>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-failsafe-plugin</artifactId>
        <configuration>
          <systemPropertyVariables>
            <test.server.port>${tomcat.http.port}</test.server.port>
          </systemPropertyVariables>
        </configuration>
      </plugin>
      ...
    </plugins>
    ...
  </build>

You can now retrieve the test.server.port system property in any of your integration test to create a proper URL to the server.