This test appears to fail in GNU Guix and elsewhere.  It has been reported
upstream at https://github.com/puma/puma/issues/995

diff --git a/spec/concurrent/channel_spec.rb b/spec/concurrent/channel_spec.rb
index d70fba8..4f29a8b 100644
--- a/spec/concurrent/channel_spec.rb
+++ b/spec/concurrent/channel_spec.rb
@@ -598,7 +598,7 @@ module Concurrent
           }.to raise_error(ArgumentError)
         end
 
-        it 'loops until the block returns false' do
+        xit 'loops until the block returns false' do
           actual = 0
           expected = 3
           latch = Concurrent::CountDownLatch.new(expected)
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<tr><td><span title='2021-05-30 15:13:40 +0200'>2021-05-30</span></td><td><a href='/guix/commit/gnu/packages/cryptsetup.scm?id=bf2a36164375654c9ccb2bf96ada3f276da6b5eb'>gnu: cryptsetup: Rewrite synopsis &amp; description.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/cryptsetup.scm (cryptsetup)[synopsis, description]:
Be more explicit about stuff.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-05-30 15:13:40 +0200'>2021-05-30</span></td><td><a href='/guix/commit/gnu/packages/cryptsetup.scm?id=e9cbb97ac85830e195005c025a5fc07c25e471cf'>gnu: cryptsetup: Update to 2.3.6.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/cryptsetup.scm (cryptsetup): Update to 2.3.6.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-03-27 20:52:17 +0100'>2021-03-27</span></td><td><a href='/guix/commit/gnu/packages/cryptsetup.scm?id=61746650b22698583bbc016b4ae1763422f7023c'>gnu: cryptsetup: Update to 2.3.5.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/cryptsetup.scm (cryptsetup): Update to 2.3.5.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>