test rebuilding C module when header changes

spec/build_tests_spec.rb

@@ -11,11 +11,26 @@ describe Rscons do
     FileUtils.rm_rf('build_tests_run')
   end
 
+  def build_testdir
+    if File.exists?("build.rb")
+      system("ruby -I #{@owd}/lib -r rscons build.rb")
+    end
+  end
+
   def test_dir(build_test_directory)
     FileUtils.cp_r("build_tests/#{build_test_directory}", 'build_tests_run')
     Dir.chdir("build_tests_run")
-    if File.exists?("build.rb")
-      system("ruby -I #{@owd}/lib -r rscons build.rb")
+    build_testdir
+  end
+
+  def file_sub(fname)
+    contents = File.read(fname)
+    replaced = ''
+    contents.each_line do |line|
+      replaced += yield(line)
+    end
+    File.open(fname, 'w') do |fh|
+      fh.write(replaced)
     end
   end
 
@@ -34,4 +49,12 @@ describe Rscons do
     File.exists?('header.o').should be_true
     `./header`.should == "The value is 2\n"
   end
+
+  it 'rebuilds a C module when a header it depends on changes' do
+    test_dir('header')
+    `./header`.should == "The value is 2\n"
+    file_sub('header.h') {|line| line.sub(/2/, '5')}
+    build_testdir
+    `./header`.should == "The value is 5\n"
+  end
 end