Only try to generate html and xml coverage reports if the source .cover file exists

rakefile

@@ -26,7 +26,7 @@ PACKAGE_REPO = "packages@gp.mitx.mit.edu:/opt/pkgrepo.incoming"
 NORMALIZED_DEPLOY_NAME = DEPLOY_NAME.downcase().gsub(/[_\/]/, '-')
 INSTALL_DIR_PATH = File.join(DEPLOY_DIR, NORMALIZED_DEPLOY_NAME)
 # Set up the clean and clobber tasks
-CLOBBER.include(BUILD_DIR, REPORT_DIR, 'cover*', '.coverage', 'test_root/*_repo', 'test_root/staticfiles')
+CLOBBER.include(BUILD_DIR, REPORT_DIR, 'test_root/*_repo', 'test_root/staticfiles')
 CLEAN.include("#{BUILD_DIR}/*.deb", "#{BUILD_DIR}/util")
 
 def select_executable(*cmds)
@@ -198,21 +198,28 @@ namespace :coverage do
     desc "Build the html coverage reports"
     task :html => :report_dirs do
         TEST_TASK_DIRS.each do |dir|
-            sh("coverage html --rcfile=#{dir}/.coveragerc || echo 'Unable to build coverage html for #{dir}'")
+            report_dir = report_dir_path(dir)
+
+            if !File.file?("#{report_dir}/.coverage")
+                next
+            end
+
+            sh("coverage html --rcfile=#{dir}/.coveragerc")
         end
     end
 
     desc "Build the xml coverage reports"
     task :xml => :report_dirs do
         TEST_TASK_DIRS.each do |dir|
+            report_dir = report_dir_path(dir)
+
+            if !File.file?("#{report_dir}/.coverage")
+                next
+            end
             # Why doesn't the rcfile control the xml output file properly??
-            sh("coverage xml -o reports/#{dir}/coverage.xml --rcfile=#{dir}/.coveragerc || echo 'Unable to build coverage xml for #{dir}'")
+            sh("coverage xml -o #{report_dir}/coverage.xml --rcfile=#{dir}/.coveragerc")
         end
     end
-
-    TEST_TASK_DIRS.each do |dir|
-        CLOBBER.include("#{dir}/.coverage")
-    end
 end
 
 task :runserver => :lms