testutil: fix make_container() cleanup

During the work on PR#1752 Florian discovered that make_containers()
is broken for nested containers like:
```
with make_container(tmp_path, {"file1": "file1 from base"}) as base_tag:
    with make_container(tmp_path, {"file1": "file1 from final layer"}, base_tag) as cont_tag:
```
It errors with:
```
Error: 5b947de461ee21b858dd5b4224e80442b2f65b6410189147f2445884d9e4e3d8: image not known
```
The reason is that we work with hashes for the image and then call
`podman image rm` which by default will also remove all dangling
references. Those are defined by not having a tag and not referenced
anymore. So the inner container cleanup also removes the outter.

There are many ways to fix this, I went with re-adding tags to the
test containers because it also makes it easy for the user to see if
we left any containers (accidently) around.

osbuild/testutil/__init__.py

@@ -5,9 +5,11 @@ import contextlib
 import inspect
 import os
 import pathlib
+import random
 import re
 import shutil
 import socket
+import string
 import subprocess
 import tempfile
 import textwrap
@@ -125,6 +127,7 @@ def mock_command(cmd_name: str, script: str):
 
 @contextlib.contextmanager
 def make_container(tmp_path, fake_content, base="scratch"):
+    fake_container_tag = "osbuild-test-" + "".join(random.choices(string.digits, k=12))
     fake_container_src = tmp_path / "fake-container-src"
     fake_container_src.mkdir(exist_ok=True)
     make_fake_tree(fake_container_src, fake_content)
@@ -134,22 +137,16 @@ def make_container(tmp_path, fake_content, base="scratch"):
     COPY . .
     """
     fake_containerfile_path.write_text(container_file_content, encoding="utf8")
-    p = subprocess.Popen([
+    subprocess.check_call([
         "podman", "build",
         "--no-cache",
+        "-t", fake_container_tag,
         "-f", os.fspath(fake_containerfile_path),
-    ], universal_newlines=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
-    while True:
-        line = p.stdout.readline()
-        if line == "":
-            break
-        print(line)
-        container_id = line.strip()
-    p.wait()
+    ])
     try:
-        yield container_id
+        yield fake_container_tag
     finally:
-        subprocess.check_call(["podman", "image", "rm", container_id])
+        subprocess.check_call(["podman", "image", "rm", fake_container_tag])
 
 
 @contextlib.contextmanager

test/mod/test_testutil_make_container.py

@@ -9,7 +9,7 @@ import pytest
 from osbuild.testutil import has_executable, make_container, mock_command
 
 
-def test_make_container_bad_podman_prints_podman_output(tmp_path, capsys):
+def test_make_container_bad_podman_prints_podman_output(tmp_path, capfd):
     fake_broken_podman = textwrap.dedent("""\
     #!/bin/sh
     echo fake-broken-podman
@@ -19,11 +19,12 @@ def test_make_container_bad_podman_prints_podman_output(tmp_path, capsys):
         with pytest.raises(subprocess.CalledProcessError):
             with make_container(tmp_path, {}) as _:
                 pass
-    assert "fake-broken-podman" in capsys.readouterr().out
+    assert "fake-broken-podman" in capfd.readouterr().out
 
 
 @pytest.mark.skipif(not has_executable("podman"), reason="no podman executable")
-def test_make_container_integration(tmp_path, capsys):
+def test_make_container_integration(tmp_path, capfd):
     with make_container(tmp_path, {"/etc/foo": "foo-content"}) as cref:
-        assert len(cref) == 64
-    assert "COMMIT" in capsys.readouterr().out
+        # names have the form "osubild-test-<random-number-of-len12>"
+        assert len(cref) == len("osbuild-test-123456789012")
+    assert "COMMIT" in capfd.readouterr().out