Mainframes handle 30 billion business transactions each day and 87% of all credit card transactions*, they are not traditionally associated with flexible, fail-fast development approaches. Can we bring the practices of agile, CI/CD and fully automated deployments to applications running on a mainframe? During our talk, we'll tell you a story about test automation; redefining the smallest testable unit of a program. And we'll discuss our learnings from introducing continuous integration and agile practices to the world of insurance and mainframes. *9 Mainframe statistics that may surprise you

1. Redefining the unit
Felix Holzäpfel-Stein & Michael Calvert
© 2020 ThoughtWorks

2. Mainframes and Cobol

3. The client context
© 2020 ThoughtWorks
Potentially shippable
increment
every 2 weeks?
Quarterly releases
with
6 weeks of
manual testing
Large insurance
with
many critical
mainframe systems
Transformation
towards
continuous and agile
software development
practices

4. ---------------------------- XConf 2020 ----------------------------
Agenda =>
0 Context
1 Finding a testable unit
2 Testing a unit
3 Conclusions
X to exit
3270 ---------------------------------------------------------------
© 2020 ThoughtWorks
June 2020
SU MO TU WE TH FR SA
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

5. © 2020 ThoughtWorks
…Modules
…10k lines
of code
…Maybe
even 30k...

6. © 2020 ThoughtWorks
…sub
programs
…up to 3k
lines of code

7. © 2020 ThoughtWorks
…sections
…isolation
not possible

8. ---------------------------- XConf 2020 ----------------------------
Agenda =>
0 Context
1 Finding a testable unit
2 Testing a unit
3 Conclusions
X to exit
3270 ---------------------------------------------------------------
© 2020 ThoughtWorks
June 2020
SU MO TU WE TH FR SA
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

9. Some things beforehand
© 2020 ThoughtWorks
No
Cobol DSL Grammar &
Parsing
NoMAINFRAME

10. Running stuff on the Mainframe is expensive
© 2020 ThoughtWorks

11. An example module
IDENTIFICATION DIVISION.
PROGRAM-ID. MY-PROGRAM.
© 2020 ThoughtWorks
Hello, XConf 2020
Enter a number:
4
Enter another number:
13
The Result is :
000000000000017
Program metadata
DATA DIVISION.
WORKING-STORAGE SECTION.
01 A-NAME PIC A(30).
01 AN-ID PIC 9(5) VALUE '12345'.
01 A-NUM PIC 9(12) VALUE '0'.
01 OTHER-NUM PIC 9(12) VALUE '0'.
01 RESULT PIC 9(15) VALUE '0'.
PROCEDURE DIVISION.
MOVE 'XConf 2020' TO A-NAME.
DISPLAY "Hello, "A-NAME.
DISPLAY "Enter a number:"
ACCEPT A-NUM.
DISPLAY "Enter another number:"
ACCEPT OTHER-NUM.
PERFORM ADD-TWO-INTS.
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
STOP RUN.
11
Variable definitions
2
2
Like a main()
function
Like calling a
function
Like defining a
function
3
4
5
3
4
5

12. Building a test driver
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
© 2020 ThoughtWorks
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
WORKING-STORAGE SECTION.
01 A-NUM PIC 9(12) VALUE '0'.
LINKAGE SECTION.
01 OTHER-NUM PIC 9(12).
PROGRAM-ID. ANOTHER-PROGRAM.
WORKING-STORAGE SECTION.
01 A-NUM EXTERNAL PIC 9(12).

13. Module
Section
Traversing the syntax tree
© 2020 ThoughtWorks
Sub program
Sub program
Section
Declaration here
Declaration here
Declaration not
really here

14. User Research
© 2020 ThoughtWorks

15. Error messages
© 2020 ThoughtWorks Images from: https://www.techrepublic.com/pictures/weird-error-messages/14/

16. Mocking
© 2020 ThoughtWorks
ADD-TWO-INTS SECTION.
ADD A-NUM OTHER-NUM GIVING RESULT.
DISPLAY "The Result is : "RESULT
CALL 'CLEAN-UP' USING A-NUM, OTHER-NUM.
PERFORM PREPARE-SOMETHING.

17. Mocking
© 2020 ThoughtWorks
MOCK SECTION PREPARE-SOMETHING
<cobol>
MOVE 0 TO A-NUM.
</cobol>
END-MOCK

18. Fast feedback loop?
© 2020 ThoughtWorks

19. We still need to parse the
entire Cobol program...
© 2020 ThoughtWorks

20. What is a mainframe?
© 2020 ThoughtWorks
Compatibility with
older systems

21. Punch cards.
© 2020 ThoughtWorks

22. ---------------------------- XConf 2020 ----------------------------
Agenda =>
0 Context
1 Finding a testable unit
2 Testing a unit
3 Conclusions
X to exit
3270 ---------------------------------------------------------------
© 2020 ThoughtWorks
June 2020
SU MO TU WE TH FR SA
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30

23. Conclusions
© 2020 ThoughtWorks
What we learnt in this wrestling match with
technology

24. Build
Collect user
feedback
Learn from
feedback
Our assumption of what a COBOL unit
test should be or look like was not what
our users needed or wanted
● Build an increment with small changes
● Actively test it in a user workshop
● Learn from and adapt to user feedback
User centric approach
© 2020 ThoughtWorks

25. How accurate do we
really need to be?
© 2020 ThoughtWorks

26. “Ambiguity? Never heard of it.”
- IBM Cobol Compiler*, 2019
© 2020 ThoughtWorks
*Not a real quote. The IBM Compiler never actually spoke these words. We’re pretty sure it was
thinking it though. Along with other evil things.

27. “Please, do not fix this [compiler]
issue. This is a programming error
that the IBM compiler does not catch
currently”
- Client Testmanager
© 2020 ThoughtWorks

28. How accurate do we
really need to be?
© 2020 ThoughtWorks

29. Actually not 100%
accurate
© 2020 ThoughtWorks

30. Fast feedback but not too expensive
© 2020 ThoughtWorks

31. Felix Holzäpfel-Stein &
Michael Calvert
Thank you
© 2020 ThoughtWorks

32. Continue the
conversation on Slack
© 2020 ThoughtWorks
XConfEurope2020
xconfeurope2020.slack.com
#talk1-redefining-the-unit
#XConfOnline