The document discusses the transformation of software development practices for large insurance clients using COBOL on mainframes, focusing on achieving continuous and agile methodologies. It highlights the challenges of testing COBOL units and emphasizes the importance of user feedback in refining approaches to incremental testing. The conclusions stress the need for adaptability based on user insights and the complexities involved in maintaining accuracy within mainframe environments.

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
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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

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Agenda =>
0 Context
1 Finding a testable unit
2 Testing a unit
3 Conclusions
X to exit
3270 ---------------------------------------------------------------
© 2020 ThoughtWorks
June 2020
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9. Some things beforehand
© 2020 ThoughtWorks
No
Cobol DSL Grammar &
Parsing
NoMAINFRAME

10. Running stuff on the Mainframe is expensive
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11. An example module
IDENTIFICATION DIVISION.
PROGRAM-ID. MY-PROGRAM.
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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
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Sub program
Sub program
Section
Declaration here
Declaration here
Declaration not
really here

14. User Research
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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...
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20. What is a mainframe?
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Compatibility with
older systems

21. Punch cards.
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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
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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?
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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?
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29. Actually not 100%
accurate
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30. Fast feedback but not too expensive
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31. Felix Holzäpfel-Stein &
Michael Calvert
Thank you
© 2020 ThoughtWorks

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