Maven plugin development - how to ensure building for Maven 3.0.x instead of 3.1.x?

Question 1

Ok, so I think I figured out the issue with aether: it appears to depend on which version of maven-plugin-testing-harness is being used. Version <= 2.1 seems to use sonatype aether. Using this set of dependencies resolves the aether problem:

    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-artifact</artifactId>
        <version>3.0.5</version>
    </dependency>

    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-compat</artifactId>
        <version>3.0.5</version>
    </dependency>

    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-plugin-api</artifactId>
        <version>3.0.5</version>
    </dependency>

    <dependency>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.6</version>
    </dependency> 

    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-core</artifactId>
        <version>3.0.5</version>
    </dependency>  

    <dependency>
        <groupId>org.apache.maven.plugin-tools</groupId>
        <artifactId>maven-plugin-annotations</artifactId>
        <version>3.1</version>
    </dependency>
    <dependency>
        <!-- version 2.1 uses sonatype aether. anything after 2.1 uses eclipse aether. -->
        <groupId>org.apache.maven.plugin-testing</groupId>
        <artifactId>maven-plugin-testing-harness</artifactId>
        <scope>test</scope>
        <version>2.1</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
        <scope>test</scope>
    </dependency>

Question 2

Slightly more confusingly than moving to the eclipse aether dependency, a lot of the dependencies of the maven-plugin-testing-harness had the scope changed from compile to provided which means they're not resolved by your downstream dependency.

It seems like this was actually experienced in Fedora as well, and they raised this issue with apache which hasn't had an attention in over a year...

On they apache bug, they state that you'll have to add dependencies on maven-core, maven-model, maven-aether-provider but on having a look at the dependencies of maven-plugin-testing-harness there are other provided scope dependencies.

The dependencies I had to add to persuade everything to work with plugin testing harness 3.3 were:

<dependency>
    <groupId>org.apache.maven.plugin-testing</groupId>
    <artifactId>maven-plugin-testing-harness</artifactId>
    <version>3.3.0</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.apache.maven</groupId>
    <artifactId>maven-compat</artifactId>
    <version>3.3.3</version>
</dependency>
<dependency>
    <groupId>org.apache.maven</groupId>
    <artifactId>maven-core</artifactId>
    <version>3.3.3</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>maven</groupId>
    <artifactId>maven-model</artifactId>
    <version>3.0.2.javadoc</version>
    <type>javadoc.jar</type>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.apache.maven</groupId>
    <artifactId>maven-aether-provider</artifactId>
    <version>3.3.3</version>
    <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.apache.maven</groupId>
  <artifactId>maven-plugin-api</artifactId>
  <version>3.3.3</version>
</dependency>
<dependency>
  <groupId>org.apache.maven.plugin-tools</groupId>
  <artifactId>maven-plugin-annotations</artifactId>
  <version>3.2</version>
  <scope>provided</scope>
</dependency>
<dependency>
  <groupId>org.codehaus.plexus</groupId>
  <artifactId>plexus-utils</artifactId>
  <version>3.0.15</version>
</dependency>

Question 3

So, interesting and weird enough, answers provided above didn't work for me. Did some digging around and found nothing. Finally came full circle when visited the plugin URL: http://maven.apache.org/plugin-testing/maven-plugin-testing-harness/dependency-convergence.html

The "Dependency Convergence" section provides all dependencies versions required to ensure the plugin 'lights up'. In a matter of seconds all was working. Here's a snippet of what I eventually had in my pom:

    <dependency>
        <groupId>org.apache.maven.plugin-testing</groupId>
        <artifactId>maven-plugin-testing-harness</artifactId>
        <version>3.3.0</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-compat</artifactId>
        <version>3.2.5</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-core</artifactId>
        <version>3.2.5</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-model</artifactId>
        <version>3.2.5</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-aether-provider</artifactId>
        <version>3.2.5</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.maven</groupId>
        <artifactId>maven-plugin-api</artifactId>
        <version>3.2.5</version>
    </dependency>
    <dependency>
        <groupId>org.apache.maven.plugin-tools</groupId>
        <artifactId>maven-plugin-annotations</artifactId>
        <version>3.3</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.11</version>
        <type>jar</type>
        <scope>test</scope>
    </dependency>

Hope this helps someone out there :)