Dynamic context in Rspec - don't repeat yourself

At Wednesday, November 03, 2010

ADSENSE HERE!

Advanced rspec features allow to use very effective technique to organize tests. You are able to construct and define context in more flexible way than before.
We use to have less problems with subject and behavior. And context is what testing is all about. Just because web apps manage data, behavior seriously depends on current state of the database.




Well organized contexts makes a real problem of testing. Unlike TestUnit, Rspec examples may have nested contexts and even dynamic contexts with the let feature.
In spite of lazy initialization let blocks they are defined before before each hook. Understand by example.

In this example orders should be delivered to confirmed customer account just after creation and should not be delivered if the account is not confirmed yet.

describe Order do
  context "after create" do #defining a partial context
    before(:each) do
      subject.customer.confirmed = confirmed
      subject.save!
    end

    context "when customer is confirmed" do 
      let(:confirmed) { true }
      it { should be_delivered }
    end
    
    context "when customer is not confirmed" do 
      let(:confirmed) { false }
      it { should_not be_delivered }
    end
  end
end

Here you can see the partial context definition and custom behavior in two nested context.
We can call not yet declared function and define it later and differently in different contexts.


Another example that is kind of pattern matching(erlang term), designed to test utility functions.
Suppose we have a boolean expression evaluation function:

describe Expression
  describe ".run" do

    subject { Expression.run(arg) }

    context "with '&' where both true" do
      let(:arg) { "true & true" }
      it {should be_true}
    end

    context "with '&' where one false" do
      let(:arg) { "false & true" }
      it {should be_false}
    end
    ........
  end
end

Very good strategy to run same function with different arguments.


Rspec is far ahead of all unit testing frameworks. Unlike most of Rspec clones (e.g. for other programming languages), Rspec authors got in deep to the testing problems and invent flexible and elegant syntax.

ADSENSE HERE!