[maven] Where is the list of predefined Maven properties

I think the best place to look is the Super POM.

As an example, at the time of writing, the linked reference shows some of the properties between lines 32 - 48.

The interpretation of this is to follow the XPath as a . delimited property.

So, for example:

${project.build.testOutputDirectory} == ${project.build.directory}/test-classes

And:

${project.build.directory} == ${project.basedir}/target

Thus combining them, we find:

${project.build.testOutputDirectory} == ${project.basedir}/target/test-classes

(To reference the resources directory(s), see this stackoverflow question)

<project>
    <modelVersion>4.0.0</modelVersion>
    .
    .
    .
    <build>
        <directory>${project.basedir}/target</directory>
        <outputDirectory>${project.build.directory}/classes</outputDirectory>
        <finalName>${project.artifactId}-${project.version}</finalName>
        <testOutputDirectory>${project.build.directory}/test-classes</testOutputDirectory>
        <sourceDirectory>${project.basedir}/src/main/java</sourceDirectory>
        <scriptSourceDirectory>src/main/scripts</scriptSourceDirectory>
        <testSourceDirectory>${project.basedir}/src/test/java</testSourceDirectory>
        <resources>
            <resource>
                <directory>${project.basedir}/src/main/resources</directory>
            </resource>
        </resources>
        <testResources>
            <testResource>
                <directory>${project.basedir}/src/test/resources</directory>
            </testResource>
        </testResources>
        .
        .
        .
    </build>
    .
    .
    .
</project>