Surpressing 'unknown command: “Switch to inspect mode.”' message

[hsbt]

I got the following with make test-all TESTS='test/irb/test_input_method -j12' at ruby/ruby repo.

(snip)
# Running tests:

unknown command: "Switch to inspect mode."
Finished tests in 0.187577s, 53.3114 tests/s, 239.9015 assertions/s.
10 tests, 45 assertions, 0 failures, 0 errors, 2 skips