Add to_bool tests

Author: Rebecca Turner

tests/test_converters.py

@@ -134,3 +134,28 @@ class C(object):
 
         c = C()
         assert True is c.a1 is c.a2
+
+
+class TestToBool(object):
+    def test_unhashable(self):
+        """
+        Fails if value is unhashable.
+        """
+        with pytest.raises(ValueError, match="Cannot convert value to bool"):
+            to_bool([])
+
+    def test_truthy(self):
+        """
+        Fails if truthy values are incorrectly converted.
+        """
+        assert to_bool("t")
+        assert to_bool("yes")
+        assert to_bool("on")
+
+    def test_falsy(self):
+        """
+        Fails if falsy values are incorrectly converted.
+        """
+        assert not to_bool("f")
+        assert not to_bool("no")
+        assert not to_bool("off")