Tutorials day. Erlang User Conference, 2010.

1. Testing database applications with QuickCheck
— Tutorial —
Laura M. Castro
Universidade da Coruña (Spain)
Stockholm, 15th November 2010
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2. Outline
1 What is a database application?
2 Why do DB applications require special testing?
3 The theory: how to test a database application with QuickCheck
4 The practise: testing a simple e-shop
5 Summing up
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3. What is a database application?
A database or data-intensive application is a software system which:
makes intensive use of great amounts of data,
relies on external storage sources for persistence (e.g., a database).
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4. What is a database application?
A database or data-intensive application is a software system which:
makes intensive use of great amounts of data,
relies on external storage sources for persistence (e.g., a database).
online
shop
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5. What is a database application?
A database or data-intensive application is a software system which:
makes intensive use of great amounts of data,
relies on external storage sources for persistence (e.g., a database).
online
shop
task
flow
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6. What is a database application?
A database or data-intensive application is a software system which:
makes intensive use of great amounts of data,
relies on external storage sources for persistence (e.g., a database).
online
bank
shop
app
task
flow
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7. Why do DB applications require special testing?
Database or data-intensive applications are software systems which:
impose complex constraints on the data they handle,
their correct operation depends on their enforcement.
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8. Why do DB applications require special testing?
Database or data-intensive applications are software systems which:
impose complex constraints on the data they handle,
their correct operation depends on their enforcement.
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9. Why do DB applications require special testing?
Database or data-intensive applications are software systems which:
impose complex constraints on the data they handle,
their correct operation depends on their enforcement.
These constraints are usually referred to as business rules.
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10. Business Rules
What are they?
“Statements that define or constrain some aspect of a business (. . . )
intended to assert business structure or to control or influence
behavior”
(B.R. Group, Defining Business Rules – What are they really?)
“Definitions of how the business should be carried out and
constraints on the business” (I. Sommerville, Software Engineering)
“Software is the realization of business rules”
(R.S. Pressman, Software Engineering – A practitioner’s approach)
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11. Business Rules
Where are they?
APPLICATION INTERFACE
APPLICATION BUSINESS LOGIC
STORAGE ACCESS
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12. Business Rules
Where are they?
APPLICATION INTERFACE
APPLICATION BUSINESS LOGIC
only basic
constraints STORAGE ACCESS
(E/R)
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13. Business Rules
Where are they?
APPLICATION INTERFACE
no
constraints
at all
APPLICATION BUSINESS LOGIC
only basic
constraints STORAGE ACCESS
(E/R)
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14. Business Rules
Where are they?
APPLICATION INTERFACE
APPLICATION BUSINESS LOGIC
STORAGE ACCESS
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15. Business Rules
When do we test them?
Since business rules are not located in a specific unit or component,
they are not covered by unit testing.
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16. Business Rules
When do we test them?
Since business rules are not located in a specific unit or component,
they are not covered by unit testing.
Since business rules dictate data-related constraints,
they are not the scope of integration testing.
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17. Business Rules
When do we test them?
Since business rules are not located in a specific unit or component,
they are not covered by unit testing.
Since business rules dictate data-related constraints,
they are not the scope of integration testing.
Since business rules need to be respected at all times,
they are not considered when testing the GUI.
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18. Business Rules
When do we test them?
Since business rules are not located in a specific unit or component,
they are not covered by unit testing.
Since business rules dictate data-related constraints,
they are not the scope of integration testing.
Since business rules need to be respected at all times,
they are not considered when testing the GUI.
Business rules must be tested as part of system testing.
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19. Why do DB applications require special testing?
Because of Business Rules
Therefore, database or data-intensive applications:
include business rules that put constraints on the data they handle,
business rules must be enforced by the system at all times,
location of the business rules is unclear.
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20. Why do DB applications require special testing?
Because of Business Rules
Therefore, database or data-intensive applications:
include business rules that put constraints on the data they handle,
business rules must be enforced by the system at all times,
location of the business rules is unclear.
In this tutorial, we will present a methodology to
test business rules at system testing level.
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21. The theory
How to test business rules with QuickCheck
To test that a data-intensive application complies with the data constraints
imposed by its business rules at all times, we use QuickCheck:
an automatic testing tool,
generates and runs random sequences of test cases,
when an error is found, test sequence is shrunk to return a minimal
test case.
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22. The theory
How to test business rules with QuickCheck
To test that a data-intensive application complies with the data constraints
imposed by its business rules at all times, we use QuickCheck:
an automatic testing tool,
generates and runs random sequences of test cases,
when an error is found, test sequence is shrunk to return a minimal
test case.
In the rest of the tutorial we assume familiarity with Quviq QuickCheck testing
tool. We will present the basics of how QuickCheck state machine library
works, but explaining these concepts is not the purpose of this specific tutorial.
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23. The theory
How to test business rules with QuickCheck
APPLICATION INTERFACE
APPLICATION BUSINESS LOGIC
STORAGE ACCESS
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24. The theory
How to test business rules with QuickCheck
APPLICATION INTERFACE
BR
enforced
here
APPLICATION BUSINESS LOGIC
STORAGE ACCESS
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25. The theory
How to test business rules with QuickCheck
APPLICATION INTERFACE
APPLICATION BUSINESS LOGIC
or here
STORAGE ACCESS data will be
"corrupted"
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26. The theory
How to test business rules with QuickCheck
QUICKCHECK
APPLICATION BUSINESS LOGIC
STORAGE ACCESS
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27. The theory
QuickCheck state machine library
In particular, we use QuickCheck state machine library:
mechanism to easily implement a testing state machine
(library callbacks),
the testing state machine generates and runs test sequences,
tests are sequences of calls to the functionalities under test.
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28. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
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29. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
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30. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
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31. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
Erlang User Conference (2010) Tutorial Workshop Testing DB apps with QC 12 / 23

32. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
Erlang User Conference (2010) Tutorial Workshop Testing DB apps with QC 12 / 23

33. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
Erlang User Conference (2010) Tutorial Workshop Testing DB apps with QC 12 / 23

34. The theory
How are test sequences generated?
test sequence
length reached? YES
NO
select SUCCESS
operation
preconditions hold?
FALSE
TRUE
execute
operation
postconditions hold?
TRUE FALSE
ERROR
Erlang User Conference (2010) Tutorial Workshop Testing DB apps with QC 12 / 23

35. The theory
QuickCheck statem machine skeleton
-module(test_eqc).
-include_lib("eqc/include/eqc.hrl").
-include_lib("eqc/include/eqc_statem.hrl").
-compile(export_all).
-record(state,{useful_info}).
%% Initialize the state
initial_state() ->
#state{useful_info = []}.
%% Command generator, S is the state
command(S) ->
oneof([ PUBLIC API OPERATIONS ]).
%% Next state transformation, S is the current state
next_state(S,_V,{call,_,_,_}) ->
S.
%% Precondition, checked before command is added to the command sequence
precondition(_S,{call,_,_,_}) ->
true.
%% Postcondition, checked after command has been evaluated
%% OBS: S is the state before next_state(S,_,<command>)
postcondition(_S,{call,_,_,_},_Res) ->
true.
prop_statem() ->
?FORALL(Cmds,commands(?MODULE),
begin
{H,S,Res} = run_commands(?MODULE,Cmds),
?WHENFAIL(
io:format("History: ~p~nState: ~p~nRes: ~p~n",[H,S,Res]),
Res == ok)
end).
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36. The practise
Testing a simple e-shop
Very simple online shop application:
Register new customer
Add new product to shop
Add product to cart
Remove product from cart
Place order
Cancel order
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37. The practise
UML model: main components
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38. The practise
E/R model: basic data constraints
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39. The practise
Golden business rule
Example of business rule (complex data constraint).
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40. The practise
Golden business rule
Example of business rule (complex data constraint).
Business rule
Only golden customers may
purchase golden products.
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41. The practise
Golden business rule
Example of business rule (complex data constraint).
Business rule
Only golden customers may
purchase golden products.
Business rules may be implemented in different ways. . .
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42. The practise
Golden business rule
Example of business rule (complex data constraint).
Business rule
Only golden customers may
purchase golden products.
Business rules may be implemented in different ways. . .
. . . but we only care they actually are.
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43. The practise
Hands-on time!
1 Explore the simple e-shop implementation given,
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44. The practise
Hands-on time!
1 Explore the simple e-shop implementation given,
2 inspect the simpleshop_eqc module stub
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45. The practise
Hands-on time!
1 Explore the simple e-shop implementation given,
2 inspect the simpleshop_eqc module stub
1 and fill-in the gaps,
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46. The practise
Hands-on time!
1 Explore the simple e-shop implementation given,
2 inspect the simpleshop_eqc module stub
1 and fill-in the gaps,
3 find out if business rule is respected
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47. The practise
Hands-on time!
1 Explore the simple e-shop implementation given,
2 inspect the simpleshop_eqc module stub
1 and fill-in the gaps,
3 find out if business rule is respected (and if not, fix it!).
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48. The practise
Outcome: QuickCheck statem machine skeleton for BR testing (I)
-module(testbr_eqc).
-include_lib("eqc/include/eqc.hrl").
-include_lib("eqc/include/eqc_statem.hrl").
-compile(export_all).
-record(state, {useful_info}).
initial_state() ->
#state{useful_info = []}.
command(S) ->
oneof([ PUBLIC API OPERATIONS (LOCAL WRAPPERS) ]).
next_state(S,_V,{call,_,_,_}) ->
S.
precondition(_S,{call,_,_,_}) ->
true.
postcondition(_S,{call,_,_,_},_Res) ->
true.
prop_brstatem() ->
?FORALL(Cmds, commands(?MODULE),
begin
true = check_data_invariant(),
{H, S, Res} = run_commands(?MODULE, Cmds),
Invariant = check_data_invariant(),
clean_up(S),
?WHENFAIL(io:format("H ~p~nS ~p~nRes ~p~n", [H, S, Res]),
conjunction([{test_execution, Res == ok},
{business_rules, Invariant}]))
end).
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49. The practise
Outcome: QuickCheck statem machine skeleton for BR testing (& II)
<command>_local(Args) ->
Expected = expected_result(<command>, Args),
Obtained = <command>(Args),
match(Expected, Obtained).
check_data_invariant() ->
IMPLEMENTATION OF BUSINESS RULES AS STORAGE QUERIES.
expected_result(<command>, Args) ->
QUERY STORAGE TO GUESS RESULT.
clean_up(S) ->
EMPTY STATE BETWEEN TEST SEQUENCES.
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50. Summing up
Testing of data-intensive applications
When testing database or data-intensive applications,
special attention must be paid to data-consistency business rules,
data-consistency constraints cannot always be trusted to the data
storage and can never be trusted to the user interface,
business rules implementation may be spread over the system,
system testing is the most adequate level to test for business rules
compliance.
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51. Summing up
Methodology to test BR using QuickCheck
1 Use a QuickCheck state machine,
2 keep state minimum,
3 add public API operations as commands/transitions,
use local wrappers to predict the result according to existing data,
and then match with the result actually obtained
4 specify pre- and postconditions as true,
5 formulate business rules (invariants) as queries to data storage,
6 write property checking invariants after each test sequence.
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52. Summing up
I hope this tutorial has been useful!
Attendants ! thanks
Get help subscribing to: quickcheck-questions@quviq.com
Material for images came from: openclipart.org, kde-look.org
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