Add UUID fixture

stix2/test/test_stix2.py

@@ -1,6 +1,7 @@
 """Tests for the stix2 library"""
 
 import datetime
+import uuid
 
 import pytest
 import pytz
@@ -24,6 +25,29 @@ def clock(monkeypatch):
     monkeypatch.setattr(datetime, 'datetime', mydatetime)
 
 
+@pytest.fixture
+def uuid4(monkeypatch):
+    def wrapper():
+        data = [0]
+
+        def wrapped():
+            data[0] += 1
+            return "00000000-0000-0000-0000-00000000%04x" % data[0]
+
+        return wrapped
+    monkeypatch.setattr(uuid, "uuid4", wrapper())
+
+
+def test_my_uuid4_fixture(uuid4):
+    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000001"
+    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000002"
+    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000003"
+    for _ in range(256):
+        uuid.uuid4()
+    assert uuid.uuid4() == "00000000-0000-0000-0000-000000000104"
+
+
+
 @pytest.mark.parametrize('dt,timestamp', [
     (datetime.datetime(2017, 1, 1, tzinfo=pytz.utc), '2017-01-01T00:00:00Z'),
     (amsterdam.localize(datetime.datetime(2017, 1, 1)), '2016-12-31T23:00:00Z'),