Sometimes, you want your code to fail. You want to make sure that in the event of a failure, an exception is generated - the equivalent of a controlled explosion. Something you can design contingencies around. Until now I’ve been a little frustrated with testing these eventualities, so I decided to hack up a quick custom assertion for your Test::Unit suites (although it should translate pretty effortlessly to RSpec or any other test framework):
# In test_helper.rb:
def assert_error_raised(errorklass=StandardError, &block)
raised = false
begin
block.call
rescue errorklass
raised = true
end
# You will see this message if an error was not raised.
# If an error was raised which was not of the type you specified, then the test trace
# will be allowed to display the error as normal and the test will fail with an E.
assert raised, "Expected error #{errorklass.to_s} to be raised but error never encountered."
end
# In your application code, let's say some_model.rb:
def do_something_with(array)
unless array.is_a?(Array)
raise ArgumentError, "Argument of type #{array.class.to_s} given to SomeModel#do_something when argument must be of type Array"
end
continue_doing_something
end
# In your test suite:
def test_error_generated_with_bad_argument_to_do_something_with
@some_model = SomeModel.new
# This test will pass
assert_error_raised(ArgumentError) do
@some_model.do_something_with "i'm not an array"
end
# This test will fail and dump the error via your test console's usual channel
assert_error_raised(RuntimeError) do
@some_model.do_something_with "neither am i"
end
end
