add brief testing docs

doc/RspecTesting.md

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+## Testing with RSpec
+
+RSpec is a ruby gem that allows you to test your code base. This is great - every time you make a change, you can do some basic sanity checks to make sure you didn't break anything.
+
+To test Metamaps, run `rspec` in the top level directory. It will automatically search the `spec` directory for files called `*_spec.rb`, and run them as tests. When it's done testing, it will print a report telling you how many tests failed. With luck, the number will be 0.
+
+At the time of writing, there are four directories in the spec folder. One, `support`, is for helper functions. `rails_helper.rb` and `spec_helper.rb` are also for helper functions.
+
+`factories` is for a gem called [factory-girl][factory-girl]. This gem lets you use the `create` and `build` functions to quickly create the simplest possible valid version of a given model. For instance:
+
+    let(:map1) { create :map }
+    let(:ronald) { create :user, name: "Ronald" }
+    let(:map2) { create :map, user: ronald }
+
+As you can see, you can also customize the factories. You can read the full documentation at the link above or check the existing specs to see how it works. It is worth reading through the factories to see how they are defined. If you add a model, please create a factory for it that defines the minimum valid state for that model.
+
+Finally, `models` and `controllers` have the actual spec files. Writing specs is usually fairly simple but you do need to understand the syntax. You can read more at [rspec.info][rspec-docs].
+
+If you modify the metamaps codebase, please consider adding tests. This will help in a few ways:
+
+ - Unrelated changes in the future that break your code will be spotted earlier
+ - Your changes will be more easily understood, since the *purpose* will be described by the spec
+
+Happy testing!
+
+[factory-girl]: https://github.com/thoughtbot/factory_girl
+[rspec-docs]: http://rspec.info