diff --git a/rakelib/acceptance_test.rake b/rakelib/acceptance_test.rake
index 2c3764ee85..290fdac01f 100644
--- a/rakelib/acceptance_test.rake
+++ b/rakelib/acceptance_test.rake
@@ -80,11 +80,15 @@ namespace :test do
             end
 
             desc "Run acceptance tests for the #{system} without collectstatic or db migrations"
-            task "#{system}:fast", [:harvest_args] => [
-                :clean_reports_dir, ACCEPTANCE_REPORT_DIR,
-            ] do |t, args|
+            task "#{system}:fast", [:harvest_args] => [:clean_reports_dir, ACCEPTANCE_REPORT_DIR] do |t, args|
                 args.with_defaults(:harvest_args => '')
-                run_acceptance_tests(system, args.harvest_args)
+
+                begin
+                    run_acceptance_tests(system, args.harvest_args)
+                ensure
+                    Rake::Task[:'test:clean_mongo'].reenable
+                    Rake::Task[:'test:clean_mongo'].invoke
+                end
             end
         end
     end
diff --git a/rakelib/tests.rake b/rakelib/tests.rake
index e77f129280..559fd2acca 100644
--- a/rakelib/tests.rake
+++ b/rakelib/tests.rake
@@ -79,7 +79,15 @@ TEST_TASK_DIRS = []
     # messing with static files.
     task "fasttest_#{system}", [:test_id] => [test_id_dir, report_dir, :clean_reports_dir] do |t, args|
         args.with_defaults(:test_id => nil)
-        run_tests(system, report_dir, args.test_id)
+
+
+
+        begin
+            run_tests(system, report_dir, args.test_id)
+        ensure
+            Rake::Task[:'test:clean_mongo'].reenable
+            Rake::Task[:'test:clean_mongo'].invoke
+        end
     end
 
     task :fasttest => "fasttest_#{system}"
@@ -97,13 +105,18 @@ Dir["common/lib/*"].select{|lib| File.directory?(lib)}.each do |lib|
 
     desc "Run tests for common lib #{lib}"
     task "test_#{lib}", [:test_id] => [
-        test_id_dir, report_dir, :clean_test_files,
-        :clean_reports_dir, :install_prereqs
+        test_id_dir, report_dir, :clean_test_files, :clean_reports_dir, :install_prereqs
     ] do |t, args|
+
         args.with_defaults(:test_id => lib)
         ENV['NOSE_XUNIT_FILE'] = File.join(report_dir, "nosetests.xml")
         cmd = "nosetests --id-file=#{test_ids} #{args.test_id}"
-        test_sh(lib, run_under_coverage(cmd, lib))
+        begin
+            test_sh(lib, run_under_coverage(cmd, lib))
+        ensure
+            Rake::Task[:'test:clean_mongo'].reenable
+            Rake::Task[:'test:clean_mongo'].invoke
+        end
     end
     TEST_TASK_DIRS << lib
 
@@ -128,6 +141,11 @@ end
 namespace :test do
     desc "Run all python tests"
     task :python, [:test_id]
+
+    desc "Drop Mongo databases created by the test suite"
+    task :clean_mongo do
+        sh("mongo #{REPO_ROOT}/scripts/delete-mongo-test-dbs.js")
+    end
 end
 
 desc "Build the html, xml, and diff coverage reports"
diff --git a/scripts/delete-mongo-test-dbs.js b/scripts/delete-mongo-test-dbs.js
new file mode 100644
index 0000000000..251ed229b4
--- /dev/null
+++ b/scripts/delete-mongo-test-dbs.js
@@ -0,0 +1,24 @@
+/*
+Drop all Mongo test databases.
+
+Usage example:
+
+    mongo delete-mongo-test-dbs.js
+
+will drop every database that starts with "test_" or "acceptance_",
+but ignore other databases.
+*/
+
+
+String.prototype.startsWith = function(substring) {
+    return (this.indexOf(substring) == 0);
+}
+
+var dbNameList = db.getMongo().getDBNames();
+for (var i in dbNameList) {
+    if (dbNameList[i].startsWith('test_') || dbNameList[i].startsWith('acceptance_')) {
+        dbToDrop = db.getMongo().getDB(dbNameList[i]);
+        print("Dropping test db " + dbNameList[i]);
+        dbToDrop.dropDatabase();
+    }
+}