calculator.rb

class Calculator
  def equation(val1, val2)
    result = val1 + val2
    return result
  end
end

# Okay so the only real point here is one of style. In Ruby it's not necessary
# to use 'return'. By default a method returns the value of the last expression
# evaluated. So your method can be rewritten

def equation( val1, val2 )
  val1 + val2
end

calculator_spec.rb

require 'calculator'


describe Calculator do
  it "should perform calculations" do    
    calc = Calculator.new
    result = calc.equation(1, 5)
    result.should == 6
  end
end

# Again it's a matter of style and each case is different by I would write this

calc.equation(1,5).should == 6

# Assignment to temporary variables is sometimes helpful but, generally, I do it
# after the fact in order to simplify an expression group that has gotten
# complex, or to cache a value that is *known* to be expensive to compute. You
# could even take it a step further and write

Calculator.new.equation(1,5).should == 6

# but I think that's a little bit ugly. On the other hand the creation of the
# calculator test asset might be better done elsewhere. Tough to say.