diff --git a/spec/rscons/environment_spec.rb b/spec/rscons/environment_spec.rb
index dc81980..2579d33 100644
--- a/spec/rscons/environment_spec.rb
+++ b/spec/rscons/environment_spec.rb
@@ -28,6 +28,14 @@ module Rscons
         env.builders.find {|name, builder| name == "Program"}.should_not be_nil
         env.builders.find {|name, builder| name == "Library"}.should be_nil
       end
+
+      context "when a block is given" do
+        it "yields self and invokes #process()" do
+          env = Environment.new do |env|
+            env.should_receive(:process)
+          end
+        end
+      end
     end
 
     describe "#clone" do
@@ -39,6 +47,15 @@ module Rscons
         env["CPPPATH"].should == ["path1"]
         env2["CPPPATH"].should == ["path1", "path2"]
       end
+
+      context "when a block is given" do
+        it "yields self and invokes #process()" do
+          env = Environment.new
+          env.clone do |env2|
+            env2.should_receive(:process)
+          end
+        end
+      end
     end
 
     describe "#add_builder" do
@@ -228,6 +245,25 @@ module Rscons
       end
     end
 
+    describe "#run_builder" do
+      it "tweaks the construction variables using given tweakers and invokes the builder" do
+        env = Environment.new
+        env.add_tweaker do |build_op|
+          if build_op[:sources].first =~ %r{src/special}
+            build_op[:vars]["CFLAGS"] += ["-O3", "-DSPECIAL"]
+          end
+        end
+        env.builders["Object"].stub(:run) do |target, sources, cache, env, vars|
+          vars["CFLAGS"].should == []
+        end
+        env.run_builder(env.builders["Object"], "build/normal/module.o", ["src/normal/module.c"], "cache", {})
+        env.builders["Object"].stub(:run) do |target, sources, cache, env, vars|
+          vars["CFLAGS"].should == ["-O3", "-DSPECIAL"]
+        end
+        env.run_builder(env.builders["Object"], "build/special/module.o", ["src/special/module.c"], "cache", {})
+      end
+    end
+
     describe ".parse_makefile_deps" do
       it 'handles dependencies on one line' do
         File.should_receive(:read).with('makefile').and_return(<<EOS)