tests: Rename test scripts, changing - to _ for consistency.

From now on, all new tests must use underscore.

Addresses issue #727.

tests/basics/class_contains.py

@@ -0,0 +1,23 @@
+# A contains everything
+class A:
+    def __contains__(self, key):
+        return True
+
+a = A()
+print(True in a)
+print(1 in a)
+print(() in a)
+
+# B contains given things
+class B:
+    def __init__(self, items):
+        self.items = items
+    def __contains__(self, key):
+        return key in self.items
+
+b = B([])
+print(1 in b)
+b = B([1, 2])
+print(1 in b)
+print(2 in b)
+print(3 in b)