CheckstyleBear.py: Add configuration check

Add invalid_config function to CheckstyleBear.py
Add tests to invalid configurations

Closes coala#898

bears/java/CheckstyleBear.py

@@ -10,6 +10,11 @@
     "geosoft": "http://geosoft.no/development/geosoft_checks.xml"}
 
 
+def invalid_configuration(checkstyle_configs, use_spaces, indent_size):
+    return (checkstyle_configs == 'google' and
+            (not use_spaces or indent_size != 2))
+
+
 def known_checkstyle_or_path(setting):
     if str(setting) in known_checkstyles.keys():
         return str(setting)
@@ -43,8 +48,9 @@ def setup_dependencies(self):
             "checkstyle.jar")
 
     def create_arguments(
-            self, filename, file, config_file,
-            checkstyle_configs: known_checkstyle_or_path="google"):
+        self, filename, file, config_file,
+        checkstyle_configs: known_checkstyle_or_path="google",
+        use_spaces: bool=True, indent_size: int = 2):
         """
         :param checkstyle_configs:
             A file containing configs to use in ``checkstyle``. It can also
@@ -64,6 +70,9 @@ def create_arguments(
             - geosoft - The Java style followed by GeoSoft. More info at
               <http://geosoft.no/development/javastyle.html>
         """
+        if invalid_configuration(checkstyle_configs, use_spaces, indent_size):
+            raise ValueError('Invalid configuration! Cannot proceed.')
+
         if checkstyle_configs in known_checkstyles:
             checkstyle_configs = self.download_cached_file(
                 known_checkstyles[checkstyle_configs],

tests/java/CheckstyleBearTest.py

@@ -30,6 +30,18 @@ def test_known_configs(self):
         self.section["checkstyle_configs"] = "google"
         self.check_validity(self.uut, [], self.good_file)
 
+    def test_config_failure_use_spaces(self):
+        self.section["checkstyle_configs"] = "google"
+        self.section.append(Setting('use_spaces', False))
+        with self.assertRaises(AssertionError):
+            self.check_validity(self.uut, [], self.good_file)
+
+    def test_config_failure_indent_size(self):
+        self.section["checkstyle_configs"] = "google"
+        self.section.append(Setting('indent_size', 3))
+        with self.assertRaises(AssertionError):
+            self.check_validity(self.uut, [], self.good_file)
+
     def test_with_custom_configfile(self):
         self.section["checkstyle_configs"] = self.empty_config
         self.check_validity(self.uut, [], self.good_file)