tests: rework testnet

Inheritance was overkill here, and now we can use inheritance for new functionality X
without having to create classes for all combinations of {X, is_testnet}.

electrum/tests/__init__.py

@@ -36,8 +36,21 @@ class SequentialTestCase(unittest.TestCase):
 class ElectrumTestCase(SequentialTestCase):
     """Base class for our unit tests."""
 
+    TESTNET = False
     # maxDiff = None
 
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        if cls.TESTNET:
+            constants.set_testnet()
+
+    @classmethod
+    def tearDownClass(cls):
+        super().tearDownClass()
+        if cls.TESTNET:
+            constants.set_mainnet()
+
     def setUp(self):
         super().setUp()
         self.asyncio_loop, self._stop_loop, self._loop_thread = util.create_and_start_event_loop()
@@ -50,20 +63,6 @@ class ElectrumTestCase(SequentialTestCase):
         shutil.rmtree(self.electrum_path)
 
 
-class TestCaseForTestnet(ElectrumTestCase):
-    """Class that runs member tests in testnet mode"""
-
-    @classmethod
-    def setUpClass(cls):
-        super().setUpClass()
-        constants.set_testnet()
-
-    @classmethod
-    def tearDownClass(cls):
-        super().tearDownClass()
-        constants.set_mainnet()
-
-
 def as_testnet(func):
     """Function decorator to run a single unit test in testnet mode.