require 'rake/testtask'

lib_dir  = File.expand_path('lib')
test_dir = File.expand_path('test')

Rake::TestTask.new("test") do |t|
  t.libs    = [lib_dir, test_dir]
  t.pattern = "test_*.rb"
  t.warning = true
end



Directory layout:

Rakefile
lib/foo.rb
test/test_foo.rb




Rake output:

maasha@mel:~/biopieces/code_ruby/Maasha$ rake
(in /Users/maasha/biopieces/code_ruby/Maasha)
rake aborted!
Don't know how to build task 'default'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:1720:in `[]'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2040:in `invoke_task'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2019:in `block (2 levels) in top_level'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2019:in `each'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2019:in `block in top_level'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2058:in `standard_exception_handling'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:2013:in `top_level'
/Users/maasha/maasha_install/lib/ruby/1.9.1/rake.rb:1992:in `run'
/Users/maasha/maasha_install/bin/rake:31:in `<main>'