Gotcha: NoMethodError: undefined method RuntimeError

So... I wrote some code in a plain-ruby class that raised a RuntimeError somewhat like below:

    class MyClass
      def initialize(opts = {})
         # do stuff
         thing = opts[:thing]
         raise RuntimeError "must have a thing!" unless thing.present? && thing.is_a?(Thing)
         # more stuff
      end
    end

and when I ran my fresh new rspec spec over it -> which looks somewhat like:

    it "should raise an error if we don't pass a thing" do
      lambda {
        my_class = MyClass.new(:thing => nil)
      }.should raise_exception(RuntimeError)
    end

I kept getting something weird:

    expected RuntimeError, got 
    #<NoMethodError: undefined method `RuntimeError' for #<MyClass:0xb5acbf9c>>

You may already have spotted the problem... ah, single-character bugs, doncha love em?

Here it is.

WRONG:

     raise RuntimeError "must have a thing!" unless thing.present? && thing.is_a?(Thing)

RIGHT:

     raise RuntimeError, "must have a thing!" unless thing.present? && thing.is_a?(Thing)

of course, you can also just go ahead and leave out the RuntimeError entirely:

     raise "must have a thing!" unless thing.present? && thing.is_a?(Thing)

because it's the default anyways... which makes it nice and defaultish for you.

rails gotchas: undefined method `expects'

If you've just installed rails edge and run the tests, they may fail with: NoMethodError: undefined method `expects' for ... etc etc over and over again (along with a few other errors).

Install the mocha gem via rubygems to get rid of a lot of these errors.

It was the line NoMethodError: undefined method `stub' for ... that clued me in.

It seems that rails requires a short list of gems/packages (beyond rails itself) simply to run its own tests... yet there is no rake gem:install task available to help you figure out which ones... and they aren't in the "contributing to rails" guide. I'll be submitting a patch shortly...

Following on from this I got:

MissingSourceFile: no such file to load -- openssl

and farther down the list:

LoadError: no such file to load -- net/https

Unfortunately, these errors occur when Ruby hasn't been installed with openssl-support. If you're running ubuntu, you can just run apt-get install libopenssl-ruby.