Env.
Jenkins Testlink Plugin - 3.7
Testlink Version - 1.9.7

Steps:

1. Create a dummy admin user with dev_key in testlink.
2. Create a dummy project in testlink
3. create testcases with Custom field. "Jenkins ID" : <unique string> in testlink
4. Make sure that all testcases are marked automated
5. Create a "Sample Test Plan" in testlink.
6. Add all the cases for execution in "Sample Test Plan"
7. Add latest jenkins testlink plugin.
8. set all valid parameters in Jenkins.
   1. testlink url = http://<servername>/testlink/lib/api/xmlrpc/v1/xmlrpc.php
   2. add valid dev key
9. Create a Jenkins task
   1. set valid parameters like project name, test plan name, custom field as Jenkins ID to the testlink build step
   2. Add valid filename for processing <junit_result>.xml with junit test method result processor having custom field as Jenkins ID.
10. Run the job

Result:

Found 0 automated test cases in TestLink.

Sorting automated test cases by TestLink test plan execution order.

Executing single Build Steps.

Executing iterative Build Steps.

Looking for the test results of TestLink test cases.

Looking for test results in JUnit methods by its name.

Found 0 test result(s).

Expected:
plugin should pick up all automated tetcases.

Python testlink api client result:

In [12]: len(tl_client.getTestCasesForTestPlan(2226,'executiontype=2'))
Out[12]: 645

In [13]: len(tl_client.getTestCasesForTestPlan(2226,'executiontype=2','buildid=9'))
Out[13]: 645

In [14]: len(tl_client.getTestCasesForTestPlan(2226,'executiontype=1','buildid=9'))
Out[14]: 0

In [15]: len(tl_client.getTestCasesForTestPlan(2226,'executiontype=2','buildid=9'))
Out[15]: 645