Grails Clover Plugin does not intercept 'testc' compiler

Grails 2.x has introduced a new compiler for building unit tests (from test/unit directory). The 'testc' task is the org.codehaus.groovy.grails.test.compiler.GrailsTestCompiler Build log looks like this:

|Compiling 1 source files
    ...
    [testc] ... \test\unit\clover\test\UnitTests.groovy

|Compiling 1 source files
   ...
  [groovyc] ... \test\integration\IntegrationServiceTests.groovy

Clover does not intercept this compiler call (it supports Groovyc, Grailsc, GrailsCompiler). As a consequence unit tests are not instrumented and not included in coverage.