test_runner: automatically rerun flaky tests (#3880)

This PR adds a plugin that automatically reruns (up to 3 times) flaky
tests. Internally, it uses data from `TEST_RESULT_CONNSTR` database and
`pytest-rerunfailures` plugin.

As the first approximation we consider the test flaky if it has failed on 
the main branch in the last 10 days.

Flaky tests are fetched by `scripts/flaky_tests.py` script (it's
possible to use it in a standalone mode to learn which tests are flaky),
stored to a JSON file, and then the file is passed to the pytest plugin.

scripts/flaky_tests.py

@@ -0,0 +1,87 @@
+#! /usr/bin/env python3
+
+import argparse
+import json
+import logging
+from collections import defaultdict
+from typing import DefaultDict, Dict
+
+import psycopg2
+import psycopg2.extras
+
+# We call the test "flaky" if it failed at least once on the main branch in the last N=10 days.
+FLAKY_TESTS_QUERY = """
+    SELECT
+        DISTINCT parent_suite, suite, test
+    FROM
+        (
+            SELECT
+                revision,
+                jsonb_array_elements(data -> 'children') -> 'name' as parent_suite,
+                jsonb_array_elements(jsonb_array_elements(data -> 'children') -> 'children') -> 'name' as suite,
+                jsonb_array_elements(jsonb_array_elements(jsonb_array_elements(data -> 'children') -> 'children') -> 'children') -> 'name' as test,
+                jsonb_array_elements(jsonb_array_elements(jsonb_array_elements(data -> 'children') -> 'children') -> 'children') -> 'status' as status,
+                to_timestamp((jsonb_array_elements(jsonb_array_elements(jsonb_array_elements(data -> 'children') -> 'children') -> 'children') -> 'time' -> 'start')::bigint / 1000)::date as timestamp
+            FROM
+                regress_test_results
+            WHERE
+                reference = 'refs/heads/main'
+        ) data
+    WHERE
+        timestamp > CURRENT_DATE - INTERVAL '%s' day
+        AND status::text IN ('"failed"', '"broken"')
+    ;
+"""
+
+
+def main(args: argparse.Namespace):
+    connstr = args.connstr
+    interval_days = args.days
+    output = args.output
+
+    res: DefaultDict[str, DefaultDict[str, Dict[str, bool]]]
+    res = defaultdict(lambda: defaultdict(dict))
+
+    logging.info("connecting to the database...")
+    with psycopg2.connect(connstr, connect_timeout=10) as conn:
+        with conn.cursor(cursor_factory=psycopg2.extras.DictCursor) as cur:
+            logging.info("fetching flaky tests...")
+            cur.execute(FLAKY_TESTS_QUERY, (interval_days,))
+            rows = cur.fetchall()
+
+    for row in rows:
+        logging.info(f"\t{row['parent_suite'].replace('.', '/')}/{row['suite']}.py::{row['test']}")
+        res[row["parent_suite"]][row["suite"]][row["test"]] = True
+
+    logging.info(f"saving results to {output.name}")
+    json.dump(res, output, indent=2)
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser(description="Detect flaky tests in the last N days")
+    parser.add_argument(
+        "--output",
+        type=argparse.FileType("w"),
+        default="flaky.json",
+        help="path to output json file (default: flaky.json)",
+    )
+    parser.add_argument(
+        "--days",
+        required=False,
+        default=10,
+        type=int,
+        help="how many days to look back for flaky tests (default: 10)",
+    )
+    parser.add_argument(
+        "connstr",
+        help="connection string to the test results database",
+    )
+    args = parser.parse_args()
+
+    level = logging.INFO
+    logging.basicConfig(
+        format="%(message)s",
+        level=level,
+    )
+
+    main(args)