Add a pair of rules to forbid flow collection styles as needed

Add a pair of new rules to forbid flow collection styles (flow mapping
and flow sequence) as needed, add those test cases and update default
configuration to disable these rules by default.

tests/test_flow_mapping.py

@@ -0,0 +1,34 @@
+# -*- coding: utf-8 -*-
+# Copyright (C) 2020 Satoru SATOH
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# pylint: disable=missing-function-docstring
+"""test cases for flow-mapping rule.
+"""
+import tests.common
+
+
+class FlowMappingTestCase(tests.common.RuleTestCase):
+    """Flow Mapping test cases.
+    """
+    rule_id = 'flow-mapping'
+
+    def test_disabled(self):
+        conf = 'flow-mapping: disable'
+        self.check('---\n'
+                   '1: {"a": 2}\n', conf)
+
+    def test_enabled(self):
+        conf = 'flow-mapping: enable\n'
+        self.check('---\n'
+                   '1: {"a": 2}\n',
+                   conf, problem1=(2, 4))
+        self.check('---\n'
+                   '1:\n'
+                   '  a: 2\n', conf)
+        self.check('---\n'
+                   '1: {\n'
+                   '  "a": 2,\n'
+                   '}\n', conf,
+                   problem1=(2, 4))

tests/test_flow_sequence.py

@@ -0,0 +1,36 @@
+# -*- coding: utf-8 -*-
+# Copyright (C) 2020 Satoru SATOH
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# pylint: disable=missing-function-docstring
+"""test cases for  flow-sequence rule.
+"""
+import tests.common
+
+
+class FlowSequenceTestCase(tests.common.RuleTestCase):
+    """Flow Sequence test cases.
+    """
+    rule_id = 'flow-sequence'
+
+    def test_disabled(self):
+        conf = 'flow-sequence: disable'
+        self.check('---\n'
+                   '1: [2, 3]\n', conf)
+
+    def test_enabled(self):
+        conf = 'flow-sequence: enable\n'
+        self.check('---\n'
+                   '1: [2, 3]\n',
+                   conf, problem1=(2, 4))
+        self.check('---\n'
+                   '1:\n'
+                   '  - 2\n'
+                   '  - 3\n', conf)
+        self.check('---\n'
+                   '[\n'
+                   '  1,\n'
+                   '  2\n'
+                   ']\n', conf,
+                   problem1=(2, 1))