Sonar report for test coverage

[Zhu, Yuxin]

Here is an instruction excerpt on how to generate test coverage report on
SonarQube dashboard.


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### Sonar Report for Test Coverage (with `jacoco` plugin)
------------------------------
1. Add a "sonar" profile in `~/.m2/settings.xml` or `project/pom.xml`
```json
<profile>
  <id>sonar</id>
  <activation>
    <activeByDefault>true</activeByDefault>
  </activation>
  <properties>
    <!--change Œlocalhost¹ & port to your SonarQube server settings -->
    <sonar.jdbc.url>jdbc:mysql://localhost:3306/sonar?</sonar.jdbc.url>
    <sonar.jdbc.username>sonar</sonar.jdbc.username>
    <sonar.jdbc.password>sonar</sonar.jdbc.password>
    <sonar.host.url>
      http://localhost:9000
    </sonar.host.url>
  </properties>
</profile>
```
2. Add `jacoco` plugin to `project/pom.xml`
```json
<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.7.4.201502262128</version>
  <executions>
    <execution>
      <id>default-prepare-agent</id>
      <goals><goal>prepare-agent</goal></goals>
    </execution>
    <execution>
      <id>default-report</id>
      <phase>prepare-package</phase>
      <goals><goal>report</goal></goals>
    </execution>
    <execution>
      <id>prepare-integration-test-agent</id>
      <goals><goal>prepare-agent-integration</goal></goals>
    </execution>
    <execution>
      <id>generate-integration-test-report</id>
      <goals><goal>report-integration</goal></goals>
    </execution>
  </executions>
</plugin>
```
3. Run maven in command line
```bash
  mvn clean test  # and/or `mvn -Plive test`
  mvn sonar:sonar
```