Duplicate test name detection

January 13, 2009 Pivotal Labs

Ruby does not throw any exceptions or warnings if an object defines two methods with the same name. The second definition always wins. While this provides great flexibility for many Ruby tasks it can be problematic when writing tests. In particular, if you define two tests with same name in the same test class, one will get run and the other will not. If you have been writing tests for a while you understand that there is nothing worse than writing a test that never gets used!

Recently Matthew O’Connor and I set out to fix this problem for Test::Unit by alias method chaining :method_added for TestCase classes and their subclasses. We use the inherited hook on Ruby classes to dynamically define a method_added hook for every test case. This is required because method_added does not get inherited between classes, so it can’t be defined only in Test::Unit::TestCase.

The following patch raises an exception if it detects a duplicated test name.

class Test::Unit::TestCase
  class << self
    def known_test_methods
      @known_test_methods ||= Array.new

    def record_test_method(method)
      if method.to_s.starts_with?("test")
        if known_test_methods.include? method
          raise "Duplicate test #{self}##{method}"
          known_test_methods << method

    def inherited(subclass)
      class << subclass
        def method_added_with_duplicate_check(method)
        alias_method_chain :method_added, :duplicate_check unless method_defined?(:method_added_without_duplicate_check)

When we first tried this against a legacy code base we found almost a dozen duplicated tests that were not running.

About the Author


Today we presented OSDV to members of Congress
Today we presented OSDV to members of Congress

Today I spent the day on Capitol Hill, presenting the Open Source Digital Voting Foundation to the 12th Ann...

Careful when doing a :include with a :has_one :through association
Careful when doing a :include with a :has_one :through association

We had an odd bug last week where we ended up with different results after we had eager loaded an associati...


Subscribe to our Newsletter

Thank you!
Error - something went wrong!