tests/functional: introduce some helpful decorators

Reduce repeated boilerplate with some helper decorators:

 @skipIfNotPlatform("x86_64", "aarch64")

  => Skip unless the build host platform matches

 @skipIfMissingCommands("mkisofs", "losetup")

  => Skips unless all listed commands are found in $PATH

 @skipIfMissingImports("numpy", "cv2")

  => Skips unless all listed modules can be imported

 @skipFlakyTest("https://gitlab.com/qemu-project/qemu/-/issues/NNN")

  => Skips unless env var requests flaky tests with the
     reason documented in the referenced gitlab bug

 @skipBigData

  => Skips unless env var permits tests creating big data files

 @skipUntrustedTest

  => Skips unless env var permits tests which are potentially
     dangerous to the host

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20241217155953.3950506-8-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/functional/qemu_test/__init__.py

@@ -13,3 +13,6 @@ from .cmd import has_cmd, has_cmds, run_cmd, is_readable_executable_file, \
     exec_command, exec_command_and_wait_for_pattern, get_qemu_img, which
 from .testcase import QemuBaseTest, QemuUserTest, QemuSystemTest
 from .linuxkernel import LinuxKernelTest
+from .decorators import skipIfMissingCommands, skipIfNotMachine, \
+    skipFlakyTest, skipUntrustedTest, skipBigDataTest, \
+    skipIfMissingImports

tests/functional/qemu_test/decorators.py

@@ -0,0 +1,107 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Decorators useful in functional tests
+
+import os
+import platform
+from unittest import skipUnless
+
+from .cmd import which
+
+'''
+Decorator to skip execution of a test if the list
+of command binaries is not available in $PATH.
+Example:
+
+  @skipIfMissingCommands("mkisofs", "losetup")
+'''
+def skipIfMissingCommands(*args):
+    def has_cmds(cmdlist):
+        for cmd in cmdlist:
+            if not which(cmd):
+                return False
+        return True
+
+    return skipUnless(lambda: has_cmds(args),
+                      'required command(s) "%s" not installed' %
+                      ", ".join(args))
+
+'''
+Decorator to skip execution of a test if the current
+host machine does not match one of the permitted
+machines.
+Example
+
+  @skipIfNotMachine("x86_64", "aarch64")
+'''
+def skipIfNotMachine(*args):
+    return skipUnless(lambda: platform.machine() in args,
+                        'not running on one of the required machine(s) "%s"' %
+                        ", ".join(args))
+
+'''
+Decorator to skip execution of flaky tests, unless
+the $QEMU_TEST_FLAKY_TESTS environment variable is set.
+A bug URL must be provided that documents the observed
+failure behaviour, so it can be tracked & re-evaluated
+in future.
+
+Historical tests may be providing "None" as the bug_url
+but this should not be done for new test.
+
+Example:
+
+  @skipFlakyTest("https://gitlab.com/qemu-project/qemu/-/issues/NNN")
+'''
+def skipFlakyTest(bug_url):
+    if bug_url is None:
+        bug_url = "FIXME: reproduce flaky test and file bug report or remove"
+    return skipUnless(os.getenv('QEMU_TEST_FLAKY_TESTS'),
+                      f'Test is unstable: {bug_url}')
+
+'''
+Decorator to skip execution of tests which are likely
+to execute untrusted commands on the host, or commands
+which process untrusted code, unless the
+$QEMU_TEST_ALLOW_UNTRUSTED_CODE env var is set.
+Example:
+
+  @skipUntrustedTest()
+'''
+def skipUntrustedTest():
+    return skipUnless(os.getenv('QEMU_TEST_ALLOW_UNTRUSTED_CODE'),
+                      'Test runs untrusted code / processes untrusted data')
+
+'''
+Decorator to skip execution of tests which need large
+data storage (over around 500MB-1GB mark) on the host,
+unless the $QEMU_TEST_ALLOW_LARGE_STORAGE environment
+variable is set
+
+Example:
+
+  @skipBigDataTest()
+'''
+def skipBigDataTest():
+    return skipUnless(os.getenv('QEMU_TEST_ALLOW_LARGE_STORAGE'),
+                      'Test requires large host storage space')
+
+'''
+Decorator to skip execution of a test if the list
+of python imports is not available.
+Example:
+
+  @skipIfMissingImports("numpy", "cv2")
+'''
+def skipIfMissingImports(*args):
+    def has_imports(importlist):
+        for impname in importlist:
+            try:
+                import impname
+            except ImportError:
+                return False
+        return True
+
+    return skipUnless(lambda: has_imports(args),
+                      'required import(s) "%s" not installed' %
+                      ", ".join(args))