Return a copy of the original Container to test fixtures

Author: dcermak

pytest_container/container.py

@@ -6,6 +6,7 @@
 import contextlib
 import enum
 import functools
+import inspect
 import itertools
 import operator
 import os
@@ -853,6 +854,16 @@ def release_lock() -> None:
 
         extra_run_args.append(f"--cidfile={self._cidfile}")
 
+        # Create a copy of the container which was used to parametrize this test
+        cls = type(self.container)
+        constructor = inspect.signature(cls.__init__)
+        constructor.parameters
+
+        kwargs = {
+            k: v
+            for k, v in self.container.__dict__.items()
+            if k in constructor.parameters
+        }
         # We must perform the launches in separate branches, as containers with
         # port forwards must be launched while the lock is being held. Otherwise
         # another container could pick the same ports before this one launches.
@@ -864,20 +875,26 @@ def release_lock() -> None:
                 for new_forward in self._new_port_forwards:
                     extra_run_args += new_forward.forward_cli_args
 
-                launch_cmd = self.container.get_launch_cmd(
+                kwargs["forwarded_ports"] = self._new_port_forwards
+                ctr = cls(**kwargs)
+
+                launch_cmd = ctr.get_launch_cmd(
                     self.container_runtime, extra_run_args=extra_run_args
                 )
 
                 _logger.debug("Launching container via: %s", launch_cmd)
                 check_output(launch_cmd)
         else:
-            launch_cmd = self.container.get_launch_cmd(
+            ctr = cls(**kwargs)
+            launch_cmd = ctr.get_launch_cmd(
                 self.container_runtime, extra_run_args=extra_run_args
             )
 
             _logger.debug("Launching container via: %s", launch_cmd)
             check_output(launch_cmd)
 
+        self.container = ctr
+
         with open(self._cidfile, "r", encoding="utf8") as cidfile:
             self._container_id = cidfile.read(-1).strip()
 

source/fixtures.rst

@@ -2,6 +2,33 @@ Fixtures
 ========
 
 
+Container class handling
+------------------------
+
+Containers are defined as instances of
+:py:class:`~pytest_container.container.Container` and
+:py:class:`~pytest_container.container.DerivedContainer`. These class instances
+are then "passed" via pytest's parametrization to the fixtures which expose the
+class instances via the
+:py:attr:`~pytest_container.container.ContainerData.container` attribute.
+
+The class instance exposed via this attribute is not guaranteed to be the
+**exact same** object as the one with which this test function was parametrized!
+The fixtures *might* only return copies, to prevent accidental mutation to
+cross-influence tests.
+
+For example, the following code is not guaranteed to work:
+
+.. code-block:: python
+
+   CTR = Container(url="registry.opensuse.org/opensuse/tumbleweed:latest")
+
+   @pytest.mark.parametrize("container", [CTR], indirect=True)
+   def test_tw_ids(container: ContainerData) -> None:
+       # this might or might not fail
+       assert id(CTR) == id(container.container)
+
+
 Handling Healthcheck
 --------------------