Add an explicit system test for processes on unix systems (#20320)

Some fields are only available on some operating systems, and for
processes Metricbeat has permissions to read. Check these fields only
on these operating systems and on processes owned by the same user
running the test.

Fix also check on current working directory.

metricbeat/module/system/test_system.py

@@ -392,41 +392,85 @@ def test_process(self):
         self.assertGreater(len(output), 0)
 
         found_cmdline = False
-        found_env = False
+        for evt in output:
+            process = evt["system"]["process"]
+            found_cmdline |= "cmdline" in process
+
+            # Remove 'env' prior to checking documented fields because its keys are dynamic.
+            process.pop("env", None)
+            self.assert_fields_are_documented(evt)
+
+            # Remove optional keys.
+            process.pop("cgroup", None)
+            process.pop("fd", None)
+            process.pop("cmdline", None)
+
+            self.assertCountEqual(SYSTEM_PROCESS_FIELDS, process.keys())
+
+        self.assertTrue(found_cmdline, "cmdline not found in any process events")
+
+    @unittest.skipUnless(re.match("(?i)linux|darwin|freebsd", sys.platform), "os")
+    def test_process_unix(self):
+        """
+        Test system/process output for fields specific of unix systems.
+        """
+        import getpass
+
+        self.render_config_template(
+            modules=[{
+                "name": "system",
+                "metricsets": ["process"],
+                "period": "5s",
+                "extras": {
+                    "process.env.whitelist": ["PATH"],
+                    "process.include_cpu_ticks": True,
+
+                    # Remove 'percpu' prior to checking documented fields because its keys are dynamic.
+                    "process.include_per_cpu": False,
+                },
+            }],
+            # Some info is only guaranteed in processes with permissions, check
+            # only on own processes.
+            processors=[{
+                "drop_event": {
+                    "when": "not.equals.user.name: " + getpass.getuser(),
+                },
+            }],
+        )
+        proc = self.start_beat()
+        self.wait_until(lambda: self.output_lines() > 0)
+        proc.check_kill_and_wait()
+        self.assert_no_logged_warnings()
+
+        output = self.read_output_json()
+        self.assertGreater(len(output), 0)
+
         found_fd = False
+        found_env = False
         found_cwd = not sys.platform.startswith("linux")
         for evt in output:
+            found_cwd |= "working_directory" in evt["process"]
+
             process = evt["system"]["process"]
+            found_fd |= "fd" in process
+            found_env |= "env" in process
 
             # Remove 'env' prior to checking documented fields because its keys are dynamic.
             env = process.pop("env", None)
-            if env is not None:
-                found_env = True
-
             self.assert_fields_are_documented(evt)
 
             # Remove optional keys.
             process.pop("cgroup", None)
-            cmdline = process.pop("cmdline", None)
-            if cmdline is not None:
-                found_cmdline = True
-            fd = process.pop("fd", None)
-            if fd is not None:
-                found_fd = True
-            cwd = process.pop("cwd", None)
-            if cwd is not None:
-                found_cwd = True
+            process.pop("cmdline", None)
+            process.pop("fd", None)
 
             self.assertCountEqual(SYSTEM_PROCESS_FIELDS, process.keys())
 
-        self.assertTrue(found_cmdline, "cmdline not found in any process events")
-
-        if sys.platform.startswith("linux") or sys.platform.startswith("freebsd"):
+        if not sys.platform.startswith("darwin"):
             self.assertTrue(found_fd, "fd not found in any process events")
 
-        if sys.platform.startswith("linux") or sys.platform.startswith("freebsd")\
-                or sys.platform.startswith("darwin"):
-            self.assertTrue(found_env, "env not found in any process events")
+        self.assertTrue(found_env, "env not found in any process events")
+        self.assertTrue(found_cwd, "working_directory not found in any process events")
 
     @unittest.skipUnless(re.match("(?i)win|linux|darwin|freebsd", sys.platform), "os")
     def test_process_metricbeat(self):