create rspec environment for build tests

spec/build_tests_spec.rb

@@ -0,0 +1,30 @@
+require 'fileutils'
+
+describe Rscons do
+  before(:all) do
+    FileUtils.rm_rf('build_tests_run')
+    FileUtils.cp_r('build_tests', 'build_tests_run')
+    @owd = Dir.pwd
+  end
+
+  after(:each) do
+    Dir.chdir(@owd)
+  end
+
+  def test_dir(build_test_directory)
+    Dir.chdir("build_tests_run/#{build_test_directory}")
+    if File.exists?('build.rb')
+      system('ruby build.rb')
+    end
+  end
+
+  ###########################################################################
+  # Tests
+  ###########################################################################
+
+  it 'builds a C program with one source file' do
+    test_dir('simple')
+    File.exists?('simple.o').should be_true
+    `./simple`.should == "This is a simple C program\n"
+  end
+end