Added approaches to move loganalyzer to pytest.

doc/loganalyzer_to_pytest.md

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+#### Requirements
+Move existed loganalyzer to be supported by pytest framework.
+
+#### Overview
+At this approach all the work will be done on the Ansible host in comparing with current implementation, so script will download extracted syslog file to the Ansible host.
+Functionality will give possibility to:
+- Add start marker to the DUT syslog. Start Marker will be automatically generated based on the prefix + date. Start marker format will be kept the same as in current implementation
+- Configure regular expressions which will be used to found matches in the syslog logs
+- Extract DUT syslog based on the markers. Download extracted logs to the Ansible host
+- Perform analysis of downloaded syslog and return the result
+
+Current loganalyzer implementation description:
+https://github.com/Azure/SONiC/wiki/LogAnalyzer
+
+#### Development
+Module "loganalyzer.py" with class "Loganalyzer".
+
+"Loganalyzer" class interface:
+- __init__(ansible_host: ansible_host, run_dir="/tmp")
+- load_common_config() - Clear previous configured match, expect and ignore. Load regular expressions from common configuration files: match, expect and ignore which are located in some configuration directory or with current module. Save loaded configuration to the self.match_regex, self.expect_regex and self.ignore_regex attributes.
+- parse_regexp_file(file_path) - Read and parse regular expressions from specified file. Return list of strings of defined regular expressions.
+- run_cmd(callable, *args, **kwargs) - Call function and analyze DUT syslog during function execution. Return the same result as "analyze" function.
+- init(marker_prefix: string) - Add start marker to the DUT syslog. Generated marker format: marker_prefix + "%Y-%m-%d-%H:%M:%S"
+- analyze() - Extract syslog based on the start marker and copy it to ansible host. Analyze extracted syslog file localy. Return python dictionary object.
+Return example:
+{"counters": {"match": 1, "expected_match": 0, "expected_missing_match": 0},
+ "match_files": {"/tmp/syslog": {"match": 0, "expected_match": 32},
+					"/tmp/syslog1": {"match": 0, "expected_match": 15}
+						},
+ "match_messages": {"/tmp/syslog1": ["Message 1", "Message 2", "Message n"],
+						 "/tmp/syslog2": ["Message 1", "Message 2", "Message n"]
+						 }
+}
+- save_full_log(dest_path) - Download extracted DUT syslog (/tmp/syslog) to the Ansible host folder specified in 'dest_path' input parameter.
+
+Attributes:
+- match_regex - list of regular expression strings to match
+- expect_regex - list of regular expression strings to expect
+- ignore_regex - list of regular expression strings to ignore
+
+Usage example:
+
+	from ansible_host import ansible_host
+	from loganalyzer import Loganalyzer
+
+	def test(localhost, ansible_adhoc, testbed):
+		hostname = testbed['dut']
+		ans_host = ansible_host(ansible_adhoc, hostname)
+
+		loganalyzer = Loganalyzer(ans_host)
+
+		# If it is a need to load common search regular expressions. It will load regexp from common files and store values in the match_regex, expect_regex and ignore_regex attributes.
+		loganalyzer.load_common_config()
+
+		# Add start marker to DUT syslog
+		loganalyzer.init()
+
+		# Example: If test need specific search marker it can be added
+		loganalyzer.match.append("Runtime error: can't parse mac address 'None'")
+
+		# Example: Get current match regular expressions
+		print(loganalyzer.match_regex)
+
+		# Example: Remove specific match regular expression
+		loganalyzer.match_regex.remove("Runtime error: can't parse mac address 'None'")
+
+		# Example: read test specific match file and add read strings to the existed match list
+		loganalyzer.match_regex.extend(loganalyzer.parse_regexp_file("PATH_TO_THE_FILE/FILE.txt"))
+
+		# Execute test steps here...
+
+		result = loganalyzer.analyze()
+		assert result["counters"]["match"] == 0, "Failure message\n{}\n{}".format(result["counters"], result["match_messages"])