minor improvements to test_images integration test

Avoid using external images in test_build and test_build_cache,
check both build caching both enabled and disabled.

Author: fulminemizzega

podman/tests/integration/test_images.py

@@ -20,6 +20,7 @@
 import tarfile
 import types
 import unittest
+import random
 
 import podman.tests.integration.base as base
 from podman import PodmanClient
@@ -139,24 +140,40 @@ def test_corrupt_load(self):
         self.assertIn("payload does not match", e.exception.explanation)
 
     def test_build(self):
-        buffer = io.StringIO("""FROM quay.io/libpod/alpine_labels:latest""")
-
-        image, stream = self.client.images.build(fileobj=buffer)
+        buffer = io.StringIO("""FROM scratch""")
+        image, _ = self.client.images.build(fileobj=buffer)
         self.assertIsNotNone(image)
         self.assertIsNotNone(image.id)
 
     def test_build_cache(self):
-        """Check that building twice the same image uses caching"""
-        buffer = io.StringIO("""FROM quay.io/libpod/alpine_labels:latest\nLABEL test=value""")
+        """Check build caching when enabled
+
+           Build twice with caching enabled (default), then again with nocache
+        """
+        def look_for_cache(stream) -> bool:
+            # Search for a line with contents "-> Using cache <image id>"
+            uses_cache = False
+            for line in stream:
+                parsed = json.loads(line)['stream']
+                if "Using cache" in parsed:
+                    uses_cache = True
+                    break
+            return uses_cache
+
+        label = str(random.getrandbits(32))
+        buffer = io.StringIO(f"""FROM scratch\nLABEL test={label}""")
         image, _ = self.client.images.build(fileobj=buffer)
         buffer.seek(0)
-        _, stream = self.client.images.build(fileobj=buffer)
-        for line in stream:
-            # Search for a line with contents "-> Using cache <image id>"
-            parsed = json.loads(line)['stream']
-            if "Using cache" in parsed:
-                break
-        self.assertEqual(parsed.split()[3], image.id)
+        cached_image, stream = self.client.images.build(fileobj=buffer)
+        self.assertTrue(look_for_cache(stream))
+        self.assertEqual(cached_image.id, image.id,
+                         msg="Building twice with cache does not produce the same image id")
+        # Build again with disabled cache
+        buffer.seek(0)
+        uncached_image, stream = self.client.images.build(fileobj=buffer, nocache=True)
+        self.assertFalse(look_for_cache(stream))
+        self.assertNotEqual(uncached_image.id, image.id,
+                         msg="Building twice without cache produces the same image id")
 
     def test_build_with_context(self):
         context = io.BytesIO()