integration_tests: introduce skipping of tests by OS (#702)

This introduces an optional, more complex OS_IMAGE format (`<image
id>::<os>::<release>`) which allows the specification of the OS/OS
release which the given image ID corresponds to.  This information is
used to skip tests which do not apply to the image.
 
This commit is comprised of the following discrete changes:
* introduce the IntegrationImage class, to handle parsing and storing
   the new OS_IMAGE format
* support inferring the OS and OS release of Ubuntu series, so that we
  can continue to set OS_IMAGE to just a series name and have test
  skipping work
* add documentation on Image Selection to integration_tests.rst
* introduce the actual skipping behaviour based on OS marks
* apply the `ubuntu` mark to all tests that should be skipped on
  non-Ubuntu operating systems

1 files changed, 63 insertions, 6 deletions

diff --git a/tests/integration_tests/clouds.py b/tests/integration_tests/clouds.py
index 4d5c2c2a..8cdb3fcc 100644
--- a/tests/integration_tests/clouds.py
+++ b/tests/integration_tests/clouds.py
@@ -6,7 +6,7 @@ from pycloudlib import EC2, GCE, Azure, OCI, LXDContainer, LXDVirtualMachine
 from pycloudlib.lxd.instance import LXDInstance
 
 import cloudinit
-from cloudinit.subp import subp
+from cloudinit.subp import subp, ProcessExecutionError
 from tests.integration_tests import integration_settings
 from tests.integration_tests.instances import (
     IntegrationEc2Instance,
@@ -25,6 +25,65 @@ except ImportError:
 log = logging.getLogger('integration_testing')
 
 
+def _get_ubuntu_series() -> list:
+    """Use distro-info-data's ubuntu.csv to get a list of Ubuntu series"""
+    out = ""
+    try:
+        out, _err = subp(["ubuntu-distro-info", "-a"])
+    except ProcessExecutionError:
+        log.info(
+            "ubuntu-distro-info (from the distro-info package) must be"
+            " installed to guess Ubuntu os/release"
+        )
+    return out.splitlines()
+
+
+class ImageSpecification:
+    """A specification of an image to launch for testing.
+
+    If either of ``os`` and ``release`` are not specified, an attempt will be
+    made to infer the correct values for these on instantiation.
+
+    :param image_id:
+        The image identifier used by the rest of the codebase to launch this
+        image.
+    :param os:
+        An optional string describing the operating system this image is for
+        (e.g.  "ubuntu", "rhel", "freebsd").
+    :param release:
+        A optional string describing the operating system release (e.g.
+        "focal", "8"; the exact values here will depend on the OS).
+    """
+
+    def __init__(
+        self,
+        image_id: str,
+        os: "Optional[str]" = None,
+        release: "Optional[str]" = None,
+    ):
+        if image_id in _get_ubuntu_series():
+            if os is None:
+                os = "ubuntu"
+            if release is None:
+                release = image_id
+
+        self.image_id = image_id
+        self.os = os
+        self.release = release
+        log.info(
+            "Detected image: image_id=%s os=%s release=%s",
+            self.image_id,
+            self.os,
+            self.release,
+        )
+
+    @classmethod
+    def from_os_image(cls):
+        """Return an ImageSpecification for integration_settings.OS_IMAGE."""
+        parts = integration_settings.OS_IMAGE.split("::", 2)
+        return cls(*parts)
+
+
 class IntegrationCloud(ABC):
     datasource = None  # type: Optional[str]
     integration_instance_cls = IntegrationInstance
@@ -57,13 +116,11 @@ class IntegrationCloud(ABC):
         raise NotImplementedError
 
     def _get_initial_image(self):
-        _released_image_id = self.settings.OS_IMAGE
+        image = ImageSpecification.from_os_image()
         try:
-            _released_image_id = self.cloud_instance.released_image(
-                self.settings.OS_IMAGE)
+            return self.cloud_instance.released_image(image.image_id)
         except (ValueError, IndexError):
-            pass
-        return _released_image_id
+            return image.image_id
 
     def _perform_launch(self, launch_kwargs):
         pycloudlib_instance = self.cloud_instance.launch(**launch_kwargs)