[Impacted Area Based PR testing] Fix actually count calculation for test scripts. (#16487)

What is the motivation for this PR?
In PR #16437, we addressed the script timing issue by selecting the five most recent test plans. However, this caused an incorrect ActualCount, as it was summarizing the number of test cases instead of the test scripts. Since the number of test scripts matches the number of test plans, this PR updates the query to correctly count the test plans.

How did you do it?
Since the number of test scripts matches the number of test plans, this PR updates the query to correctly count the test plans.

Author: yutongzhang-microsoft

.azure-pipelines/impacted_area_testing/calculate_instance_number.py

@@ -88,18 +88,15 @@ def main(scripts, topology, branch):
         # As baseline test is the universal set of PR test
         # we get the historical running time of one script here
         # We get recent 5 test plans and calculate the average running time
-        query = "V2TestCases " \
-                "| join kind=inner" \
-                "(TestPlans " \
+        query = "let FilteredTestPlans = TestPlans " \
                 "| where TestPlanType == 'PR' and Result == 'FINISHED' " \
-                f"and Topology == '{PR_CHECKER_TOPOLOGY_NAME[topology][0]}' " \
-                f"and TestBranch == '{branch}' and TestPlanName contains '{PR_CHECKER_TOPOLOGY_NAME[topology][1]}' " \
-                "and TestPlanName contains '_BaselineTest_'" \
-                "| order by UploadTime desc" \
-                "| take 5) on TestPlanId " \
-                f"| where FilePath == '{script}' " \
-                "| where Result !in ('failure', 'error') " \
-                "| summarize ActualCount = count(), TotalRuntime = sum(Runtime)"
+                f"and Topology == '{PR_CHECKER_TOPOLOGY_NAME[topology][0]}'" \
+                f"and TestBranch == '{branch}' and TestPlanName contains '{PR_CHECKER_TOPOLOGY_NAME[topology][1]}'" \
+                "and TestPlanName contains '_BaselineTest_' | order by UploadTime desc | take 5;" \
+                "let FilteredCount = toscalar(FilteredTestPlans | summarize ActualCount = count());" \
+                "V2TestCases | join kind=inner( FilteredTestPlans ) on TestPlanId" \
+                f"| where FilePath == '{script}' | where Result !in ('failure', 'error')" \
+                "| summarize TotalRuntime = sum(Runtime), ActualCount=FilteredCount"
         try:
             response = client.execute("SonicTestData", query)
         except Exception as e: