diff --git a/gmailfilter/test.py b/gmailfilter/test.py
index 126af74..20cc69a 100644
--- a/gmailfilter/test.py
+++ b/gmailfilter/test.py
@@ -132,7 +132,7 @@ class SubjectContains(Test):
 
     """
 
-    def __init__(self, search_string, case_sensitive=False):
+    def __init__(self, search_string, case_sensitive=True):
         self._search_string = search_string
         self._case_sensitive = case_sensitive
 
@@ -154,7 +154,6 @@ def __init__(self, target_list):
         self._target_list = target_list
 
     def match(self, message):
-
         return get_list_id(message) == self._target_list
 
 
diff --git a/gmailfilter/tests/factory.py b/gmailfilter/tests/factory.py
index c746b8b..842da0b 100644
--- a/gmailfilter/tests/factory.py
+++ b/gmailfilter/tests/factory.py
@@ -6,7 +6,7 @@ class TestFactoryMixin(object):
 
     """A mixin class that generates test fake values."""
 
-    def get_email_message(self, headers=None):
+    def get_email_message(self, headers=None, subject='Test Subject'):
         """Get an email message.
 
         :param headers: If set, must be a dict or 2-tuple iteratble of key/value
@@ -15,6 +15,7 @@ def get_email_message(self, headers=None):
         message = FakeMessage()
         if headers:
             message.headers = dict(headers)
+        message.headers['Subject'] = subject
         return message
 
 
@@ -26,3 +27,6 @@ def __init__(self):
     def get_headers(self):
         return self.headers
 
+    def subject(self):
+        return self.get_headers()['Subject']
+
diff --git a/gmailfilter/tests/test_tests.py b/gmailfilter/tests/test_tests.py
index 0b8305c..88bb507 100644
--- a/gmailfilter/tests/test_tests.py
+++ b/gmailfilter/tests/test_tests.py
@@ -7,6 +7,7 @@
     And,
     Or,
     MatchesHeader,
+    SubjectContains,
 )
 from gmailfilter._message import Message
 
@@ -86,3 +87,39 @@ def test_fails_when_header_value_is_wrong(self):
     def test_passes_with_correct_value(self):
         message = self.get_email_message(headers=dict(SomeHeader='123'))
         self.assertTrue(MatchesHeader('SomeHeader', '123').match(message))
+
+
+class SubjectContainsTests(TestCase, TestFactoryMixin):
+
+    def test_case_sensitive_contains_matches_whole_string(self):
+        message = self.get_email_message(subject='Hello World')
+        self.assertTrue(SubjectContains('Hello World').match(message))
+
+    def test_case_sensitive_contains_matches_partial_string(self):
+        message = self.get_email_message(subject='Hello World')
+        self.assertTrue(SubjectContains('ello Worl').match(message))
+
+    def test_case_sensitive_is_the_default(self):
+        message = self.get_email_message(subject='Hello World')
+        self.assertFalse(SubjectContains('hello world').match(message))
+
+    def test_case_insensitive_works_with_ascii(self):
+        message = self.get_email_message(subject='Hello World')
+        self.assertTrue(
+            SubjectContains('hello world', case_sensitive=False).match(message)
+        )
+
+    def test_case_insensitive_works_with_unicode(self):
+        message = self.get_email_message(subject='Hello BUẞE')
+        self.assertTrue(
+            SubjectContains('hello BUSSE', case_sensitive=False).match(message)
+        )
+        self.assertTrue(
+            SubjectContains('hello Buße', case_sensitive=False).match(message)
+        )
+
+    def test_case_insensitive_works_with_unicode_accents(self):
+        message = self.get_email_message(subject='Hêllo')
+        self.assertTrue(
+            SubjectContains('h\xeallo', case_sensitive=False).match(message)
+        )