add tests for formatting

tests/test_fmt.py

@@ -0,0 +1,71 @@
+import textwrap
+
+import capa.rules
+
+EXPECTED = textwrap.dedent('''\
+   rule:
+     meta:
+       name: test rule
+       author: user@domain.com
+       scope: function
+       examples:
+         - foo1234
+         - bar5678
+     features:
+       - and:
+         - number: 1
+         - number: 2''')
+
+
+def test_rule_reformat_top_level_elements():
+    rule = textwrap.dedent('''\
+        rule:
+          features:
+            - and:
+              - number: 1
+              - number: 2
+          meta:
+            name: test rule
+            author: user@domain.com
+            scope: function
+            examples:
+              - foo1234
+              - bar5678''')
+
+    assert capa.rules.Rule.from_yaml(rule).to_yaml() == EXPECTED
+
+
+def test_rule_reformat_indentation():
+    rule = textwrap.dedent('''\
+        rule:
+         meta:
+            name: test rule
+            author: user@domain.com
+            scope: function
+            examples:
+            - foo1234
+            - bar5678
+         features:
+                - and:
+                             - number: 1
+                             - number: 2''')
+
+    assert capa.rules.Rule.from_yaml(rule).to_yaml() == EXPECTED
+
+
+def test_rule_reformat_order():
+    rule = textwrap.dedent('''\
+         rule:
+           meta:
+             author: user@domain.com
+             examples:
+               - foo1234
+               - bar5678
+             scope: function
+             name: test rule
+           features:
+             - and:
+               - number: 1
+               - number: 2''')
+
+    assert capa.rules.Rule.from_yaml(rule).to_yaml() == EXPECTED