Recursively glob for RSpec test files at runtime

I have a suite of RSpec tests I want to group under the following hierarchy:

tests/
  featA/
     t1.rb
     t2.rb
  featB/
     t3.rb

but when I run

$ rspec tests

I get the following:

rspec tests
No examples were matched. Perhaps {:unless=>#<Proc:0x00007f318919cc08@/usr/lib/ruby/gems/1.8/gems/rspec-core-2.5.1/lib/rspec/core/configuration.rb:51>, :if=>#<Proc:0x00007f318919cdc0@/usr/lib/ruby/gems/1.8/gems/rspec-core-2.5.1/lib/rspec/core/configuration.rb:50>} is excluding everything?

Finished in 0.00003 seconds
0 examples, 0 failures

I feel like I'm going mad, but there doesn't seem to be a way to get RSpec to recursively glob for test files? Does this functionality exist?

EDIT:

I have a workaround by doing this:

$ rspec `find tests -name "*.rb"`

but I suspect I shouldn't have to. Am I right?