Test code gets included in coverage report and skews coverate rate

I am using OpenClover in an Azure DevOps Pipeline.

The problem: Whereas the coverage given in target/site/clover/index.html, when I run clover locally, is (sadly) around 45%, in Azure DevOps it is at 71%.

The reason for that is that the coverage report in AzDO, which is based on target/site/clover.xml, also includes test code, which in general has a coverage of 100%, thusly skewing the result.

How can I rid the coverage report of including test code? What I have tried to no avail is using classfilters in ReportGenerator - which is responsible for converting clover.xml to Cobertura so that AzDO can interpret it. Neither of the following worked:

classfilters: '-*Test.java'
classfilters: '-*Test'
classfilters: '-*Test.class'

For context, here is my pipeline.

- task: Maven@3
  inputs:
    mavenPomFile: 'pom.xml'
    mavenOptions: '-Xmx1024m'
    mavenAuthenticateFeed: true
    javaHomeOption: 'JDKVersion'
    jdkVersionOption: '1.11'
    jdkArchitectureOption: 'x64'
    publishJUnitResults: false
    goals: 'clean clover:setup test clover:aggregate clover:clover'

- task: reportgenerator@4
  inputs:
    reports: '$(Build.SourcesDirectory)/target/site/clover/clover.xml'
    classfilters: '-*Test'
    targetdir: '$(Build.SourcesDirectory)/CoverageResults'

- task: PublishCodeCoverageResults@1
  displayName: 'Publish code coverage'
  inputs:
    codeCoverageTool: Cobertura
    summaryFileLocation: '$(Build.SourcesDirectory)/CoverageResults/Cobertura.xml'

And this is the part of the pom file relating to clover:

<build>
    <plugins>
        <plugin>
            <groupId>org.openclover</groupId>
            <artifactId>clover-maven-plugin</artifactId>
            <version>4.4.1</version>
            <executions>
                <execution>
                    <phase>generate-sources</phase>
                    <goals>
                        <goal>instrument</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

From ReportGenerator 4.6.4, test projects can be excluded without the (fragile) file filter.

- task: reportgenerator@4
  inputs:
    reports: '$(Build.SourcesDirectory)/target/site/clover/clover.xml'
    customSettings: 'settings:excludeTestProjects=true'
    targetdir: '$(Build.SourcesDirectory)/CoverageResults'