Refactor control char test

Fix test case for control chars according to the stripping/warning
changes.
Revamp using the charsethelper decoder, and add more tests

tests/resources/controlchars/controlchars_ascii_ok.js

@@ -0,0 +1 @@
+function test() {}

tests/resources/controlchars/controlchars_utf-8_ok.js

@@ -0,0 +1 @@
+function täst() {}

tests/test_controlchars.py

@@ -0,0 +1,42 @@
+import os
+
+import validator.testcases.charsethelper
+import validator.testcases.scripting
+
+# Originated from bug 626496
+
+def _do_test(path):
+    "Performs a test on a JS file"
+    script = validator.testcases.charsethelper.decode(open(path, "rb").read())
+
+    err = validator.testcases.scripting.traverser.MockBundler()
+    validator.testcases.scripting.test_js_file(err, path, script)
+
+    return err
+
+def test_controlchars_ascii_ok():
+    """Tests that multi-byte characters are decoded properly (utf-8)"""
+
+    errs = _do_test("tests/resources/controlchars/controlchars_ascii_ok.js")
+    assert len(errs.ids) == 0
+
+def test_controlchars_ascii_warn():
+    """Tests that multi-byte characters are decoded properly (utf-8)
+		but remaining non ascii characters raise warnings"""
+
+    errs = _do_test("tests/resources/controlchars/controlchars_ascii_warn.js")
+    assert len(errs.ids) == 1 and errs.ids[0][2] == "control_char_filter"
+
+def test_controlchars_utf8_ok():
+    """Tests that multi-byte characters are decoded properly (utf-8)"""
+
+    errs = _do_test("tests/resources/controlchars/controlchars_utf-8_ok.js")
+    assert len(errs.ids) == 0
+
+def test_controlchars_utf8_warn():
+    """Tests that multi-byte characters are decoded properly (utf-8)
+		but remaining non ascii characters raise warnings"""
+
+    errs = _do_test("tests/resources/controlchars/controlchars_utf-8_warn.js")
+    assert len(errs.ids) == 1 and errs.ids[0][2] == "control_char_filter"
+