Allow inheritance in tests

Closes #30.

tests/samples/test.md

@@ -1 +1,2 @@
 The quick brown fox jumps over the lazy dog.
+I used the hammer.

tests/test_dfw_uncomparables.py

@@ -1,12 +1,14 @@
 from check import Check
-from proselint.checks import dfw_uncomparables
+from proselint.checks import dfw_uncomparables as chk
 
 
 class TestCheck(Check):
 
+    __test__ = True
+
     @property
     def this_check(self):
-        return dfw_uncomparables
+        return chk
 
     def test_sample_phrases(self):
         assert not self.check(
@@ -15,5 +17,5 @@ def test_sample_phrases(self):
 
     def test_linebreaks(self):
         assert not self.check(
-            """This sentence is very\n unique."""
+            """This sentence is very\nunique."""
         )

tests/test_strunk_white_eos.py

@@ -0,0 +1,21 @@
+from check import Check
+from proselint.checks import strunk_white_eos as chk
+
+
+class TestCheck(Check):
+
+    __test__ = True
+
+    @property
+    def this_check(self):
+        return chk
+
+    def test_with_utilized(self):
+        assert self.check(
+            """I use a hammer to drive nails into wood.."""
+        )
+
+    def test_no_utilized(self):
+        assert not self.check(
+            """I utilize a hammer to drive nails into wood."""
+        )