It seems there are currently some issues building the tool on Windows, as reported in CMTOOL-303 comments:
1. "I had to build with mvn install -DskipTests as the symlinks used in tests don't work on Windows: MigrationFilesTest.copyFileWithALink:111, MigrationFilesTest.copyFileWithALinkSeveralLevels:125)"
2. I'm afraid I'm not able to fix it. As far as I now, it's a Windows issue: SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE is not enabled in the current LTS JDK and you need to have developer mode enabled.
I was able to overcome this with JDK 16. Now I got:
org.apache.maven.plugin.PluginExecutionException: Execution default of goal org.asciidoctor:asciidoctor-maven-plugin:1.5.6:process-asciidoc failed: Cannot invoke "org.jruby.RubyModule.addMethod(String, org.jruby.internal.runtime.methods.DynamicMethod)" because "proxy" is null
Changing version.org.asciidoctor.asciidoctor-maven-plugin to 1.6.0 in pom.xml fixed that. So I could build this finally without -DskipTests.