Improve Condition DSL framework:

Add the necessary API so that we can implement new tests easily as new
standalone classes.

  In Condition::DSL:

* Add #tests accessor;
* Modify constructor so that it accepts the env;
* Implement .define_test(keyword, class) method.

lib/producer/core/condition/dsl.rb

@@ -4,13 +4,23 @@ module Producer
       class DSL
         class << self
           def evaluate(env, &block)
-            dsl = new(&block)
+            dsl = new(env, &block)
             Condition.new(dsl.evaluate)
           end
+
+          def define_test(keyword, klass)
+            define_method(keyword) do |*args|
+              @tests << klass.new(@env, *args)
+            end
+          end
         end
 
-        def initialize(&block)
-          @block = block
+        attr_accessor :tests
+
+        def initialize(env, &block)
+          @env    = env
+          @block  = block
+          @tests  = []
         end
 
         def evaluate

spec/producer/core/condition/dsl_spec.rb

@@ -4,11 +4,12 @@ module Producer::Core
   describe Condition::DSL do
     let(:block)   { proc { :some_condition_code } }
     let(:env)     { double('env') }
-    subject(:dsl) { Condition::DSL.new(&block) }
+    subject(:dsl) { Condition::DSL.new(env, &block) }
 
     describe '.evaluate' do
-      it 'builds a new DSL sandbox with given code' do
-        expect(Condition::DSL).to receive(:new).with(&block).and_call_original
+      it 'builds a new DSL sandbox with given env and code' do
+        expect(Condition::DSL)
+          .to receive(:new).with(env, &block).and_call_original
         Condition::DSL.evaluate(env, &block)
       end
 
@@ -32,10 +33,53 @@ module Producer::Core
       end
     end
 
+    describe '.define_test' do
+      let(:some_test_class) { double('SomeTest class') }
+
+      before do
+        Condition::DSL.define_test(:some_test, some_test_class)
+      end
+
+      it 'defines a new test keyword' do
+        expect(dsl).to respond_to :some_test
+      end
+
+      context 'defined test keyword' do
+        let(:arguments) { [:some, :arguments] }
+
+        it 'builds a new test with the env and given arguments' do
+          expect(some_test_class).to receive(:new).with(env, arguments)
+          dsl.some_test(arguments)
+        end
+
+        it 'registers the new test' do
+          some_test = double('SomeTest instance')
+          allow(some_test_class).to receive(:new) { some_test }
+          dsl.some_test(arguments)
+          expect(dsl.tests).to include(some_test)
+        end
+      end
+    end
+
     describe '#initialize' do
       it 'assigns the code' do
         expect(dsl.instance_eval { @block }).to be block
       end
+
+      it 'assigns the env' do
+        expect(dsl.instance_eval { @env }).to be env
+      end
+
+      it 'assigns no test' do
+        expect(dsl.tests).to be_empty
+      end
+    end
+
+    describe '#tests' do
+      it 'returns the assigned tests' do
+        dsl.instance_eval { @tests = [:some_test] }
+        expect(dsl.tests).to eq [:some_test]
+      end
     end
 
     describe '#evaluate' do