[yocto-autobuilder-helper,3/3] scripts/send_qa_email: guess latest tested revision when dealing with branch

diff --git a/scripts/send_qa_email.py b/scripts/send_qa_email.py
index ac8b4716f07b..14446a274e90 100755
--- a/scripts/send_qa_email.py
+++ b/scripts/send_qa_email.py
@@ -53,7 +53,17 @@  def get_previous_tag(targetrepodir, version):
     defaultbaseversion, _, _ = utils.get_version_from_string(subprocess.check_output(["git", "describe", "--abbrev=0"], cwd=targetrepodir).decode('utf-8').strip())
     return utils.get_tag_from_version(defaultbaseversion, None)
 
-def get_regression_base_and_target(targetbranch, basebranch, release, targetrepodir):
+def get_last_tested_rev_on_branch(branch, log):
+    # Fetch latest test results revision on corresponding branch in test
+    # results repository
+    tags_list = subprocess.check_output(["git", "ls-remote", "--refs", "-t", TEST_RESULTS_REPOSITORY_URL, "refs/tags/" + branch + "/*"]).decode('utf-8').strip()
+    latest_test_tag=tags_list.splitlines()[-1].split()[1]
+    # From test results tag, extract Poky revision
+    tested_revision = re.match('refs\/tags\/.*\/\d+-g([a-f0-9]+)\/\d', latest_test_tag).group(1)
+    log.info(f"Last tested revision on branch {branch} is {tested_revision}")
+    return tested_revision
+
+def get_regression_base_and_target(targetbranch, basebranch, release, targetrepodir, log):
     if not targetbranch:
         # Targetbranch/basebranch is an arbitrary configuration (not defined in config.json): do not run regression reporting
         return None, None
@@ -63,9 +73,11 @@  def get_regression_base_and_target(targetbranch, basebranch, release, targetrepo
         # regression reporting must be done against previous tag
         return get_previous_tag(targetrepodir, release), targetbranch
     elif basebranch:
-        # Targetbranch/basebranch is defined in config.json: regression
-        # reporting must be done against branches as defined in config.json
-        return basebranch, targetbranch
+        # Basebranch/targetbranch are defined in config.json: regression
+        # reporting must be done between latest test result available on base branch
+        # and latest result on targetbranch
+        latest_tested_rev_on_basebranch = get_last_tested_rev_on_branch(basebranch, log)
+        return latest_tested_rev_on_basebranch, targetbranch
 
     #Default case: return previous tag as base
     return get_previous_tag(targetrepodir, release), targetbranch
@@ -177,7 +189,7 @@  def send_qa_email():
                 log.warning("Test results not published on release version. Faulty AB configuration ?")
 
             utils.printheader("Processing regression report")
-            regression_base, regression_target = get_regression_base_and_target(targetbranch, basebranch, args.release, targetrepodir)
+            regression_base, regression_target = get_regression_base_and_target(targetbranch, basebranch, args.release, targetrepodir, log)
             if regression_base and regression_target:
                 generate_regression_report(querytool, targetrepodir, regression_base, regression_target, tempdir, args.results_dir, log)
 
diff --git a/scripts/test_send_qa_email.py b/scripts/test_send_qa_email.py
index 74d60d55655d..5509b3c2510e 100755
--- a/scripts/test_send_qa_email.py
+++ b/scripts/test_send_qa_email.py
@@ -11,7 +11,10 @@  import os
 import sys
 import unittest
 import send_qa_email
+import logging
 
+logging.basicConfig(level=logging.INFO, format="%(levelname)s: %(message)s")
+log = logging.getLogger('send-qa-email')
 
 class TestVersion(unittest.TestCase):
     test_data_get_version = [
@@ -45,9 +48,9 @@  class TestVersion(unittest.TestCase):
         {"name": "Older release", "input": {"targetbranch": "kirkstone",
                                             "basebranch": None, "release": "yocto-4.0.8.rc2"}, "expected": ("yocto-4.0.7", "kirkstone")},
         {"name": "Master Next", "input": {"targetbranch": "master-next",
-                                          "basebranch": "master", "release": None}, "expected": ("master", "master-next")},
+                                          "basebranch": "master", "release": None}, "expected": ("LAST_TESTED_REV", "master-next")},
         {"name": "Fork Master Next", "input": {"targetbranch": "ross/mut",
-                                               "basebranch": "master", "release": None}, "expected": ("master", "ross/mut")},
+                                               "basebranch": "master", "release": None}, "expected": ("LAST_TESTED_REV", "ross/mut")},
         {"name": "Nightly a-quick", "input": {"targetbranch": "master",
                                                "basebranch": None, "release": "20230322-2"}, "expected": ("LAST_TAG", "master")},
     ]
@@ -68,11 +71,11 @@  class TestVersion(unittest.TestCase):
         for data in self.regression_inputs:
             with self.subTest(data['name']):
                 base, target = send_qa_email.get_regression_base_and_target(
-                    data['input']['targetbranch'], data['input']['basebranch'], data['input']['release'], os.environ.get("POKY_PATH"))
+                    data['input']['targetbranch'], data['input']['basebranch'], data['input']['release'], os.environ.get("POKY_PATH"), log)
                 expected_base, expected_target = data["expected"]
                 # The comparison base can not be set statically in tests when it is supposed to be the previous tag,
                 # since the result will depend on current tags
-                if expected_base == "LAST_TAG":
+                if expected_base == "LAST_TAG" or expected_base == "LAST_TESTED_REV":
                     self.assertIsNotNone(base)
                 else:
                     self.assertEqual(base, expected_base)