If a build is being built, Bamboo will ignore build trigger and not queue the build.

In case of a dependent test build, you might want plan to built for each trigger -

Bear in mind that the code can successfully build, but still fail testing. Thus the following readily occurs:

• code changes => plan A runs
• plan A completes => plan B runs
• code changes again => plan A runs
• plan A completes, plan B still running => plan B not queued
• plan B completes