We only add enableMajorityReadConcern to the command line arguments if it is set to true in the TestData. This means that mongods started test fixtures do not respect TestData.enableMajorityReadConcern="false". Passthroughs are unaffected. Instead of checking whether jsTest.options().enableMajorityReadConcern is true, we should check that it is not equal to undefined. We should also add a test to ensure that if we set TestData.enableMajorityReadConcern, then the server reports that it does not support committed reads.