spec/by_need_spec.rb in dataflow-0.1.1 vs spec/by_need_spec.rb in dataflow-0.2.0

@@ -1,12 +1,55 @@
 require "#{File.dirname(__FILE__)}/spec_helper"
 
-describe 'A by_need trigger' do
-  it 'creates a need when a method is called on it' do
-    local do |x, y, z|
-      Thread.new { unify y, by_need { 4 } }
-      Thread.new { unify z, x + y }
-      Thread.new { unify x, by_need { 3 } }      
-      z.should == 7
+describe 'A by_need expression' do
+  describe 'when a method is called on it' do
+    it 'binds its variable' do
+      local do |x, y, z|
+        Thread.new { unify y, by_need { 4 } }
+        Thread.new { unify z, x + y }
+        Thread.new { unify x, by_need { 3 } }
+        z.should == 7
+      end
+    end
+  end
+
+  describe 'when a bound variable is unified to it' do
+    it 'passes unififcation for equal values' do
+      local do |x|
+        unify x, by_need { 1 }
+        unify x, 1
+        x.should == 1
+
+        y = by_need { 1 }
+        unify y, 1
+        y.should == 1
+      end
+    end
+
+    it 'fails unififcation for unequal values' do
+      local do |x|
+        unify x, by_need { 1 }
+        lambda { unify x, 2 }.should raise_error(Dataflow::UnificationError)
+
+        y = by_need { 1 }
+        lambda { unify y, 2 }.should raise_error(Dataflow::UnificationError)
+      end
+    end
+
+    describe 'when it is unified to a bound variable' do
+      it 'passes unififcation for equal values' do
+        local do |x|
+          unify x, 1
+          unify x, by_need { 1 }
+          x.should == 1
+        end
+      end
+      
+      it 'fails unification for unequal values' do
+        local do |x|
+          unify x, 1
+          lambda { unify x, by_need { 2 } }.should raise_error(Dataflow::UnificationError)
+        end
+      end
     end
   end
 end