1. Testing a persistence layer
Chris Richardson
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

2. Copyright (c) 2006 Chris Richardson. All rights reserved.
About Chris…
Grew up in England
Live in Oakland, CA
Twenty years of software development experience
Building object-oriented software since 1986
Developing with Java since 1996
Using J2EE since 1999
Author of POJOs in Action
Run a consulting company that helps organizations build better software faster
Chair of the eBIG Java SIG (
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

3. What’s a persistence layer?
SQL-based DAOs:
Execute SQL statements
Use JDBC, iBATIS
ORM-based DAOs:
Use Hibernate, JDO or JPA
O/R mapping defined by annotations or XML
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

4. The challenge of testing
Testing is like flossing: essential to prevent software decay
But some of us find it difficult to do regularly
You need lots of tests
You want the tests to run quickly
But databases are slow
Writing database setup code can be difficult
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

5. Copyright (c) 2006 Chris Richardson. All rights reserved.
Testing strategies
Test with mocks (fast)
Test the business logic with mock DAOs
Test the DAOs with mock ORM APIs
Test the O/R mapping metadata (fast)
Verify that classes are mapped correctly
Write some database tests (slow but fewer)
Test persistent object CRUD
Test the queries
Whenever you can:
Use an in-process/memory DB such as HSQLDB
Don’t commit transactions
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

6. Pattern #0: Mock the persistent layer
Goal:
Test the business logic
But tests that use the DB are:
Slow running
Difficult to write
How:
Use fast, easy to write, in-memory tests
Use mocks for the DAOs
Works nicely with dependency injection
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

7. Pattern #1: Mock the ORM framework
DAO = class that wraps the ORM framework
Problem:
Bugs in the logic of the DAOs
Testing against the DB is slow
Solution
Use mock objects for the ORMF APIs
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

8. Pattern #2: Test the O/R mapping
Problem:
Incorrectly defined mapping, e.g. forgetting to map a field is a common bug
But tests that save objects and check the contents of the DB are slow to execute and tedious to write
Solution:
Read XML or metadata
Make assertions about the mapping
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

9. Pattern #3: Test the schema
Problem:
Object/relational mapping can reference non-existent tables and columns
Only some execution paths will access those tables and columns
Solutions:
Have the ORM validate the schema
Write a test that verifies that all referenced tables and columns exists
How
Persistence framework-specific
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

10. Pattern #4: CRUD tests for the persistent objects
Problem:
Database constraints can prevent application from updating the database
Solution
Verify that the objects can be created, updated and deleted
Each test takes an object through its lifecycle
Creates and saves an object
One or more times: Load and update it
Delete the object
These tests are slow(er)
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

11. Pattern #5: Test the queries
Problem:
Malformed queries
Logic errors in queries, e.g. < instead of <=
Solution:
Write tests for the queries
Each test:
Populates database with test objects
Execute queries with parameters
Verify that the query returns the expected result
These tests can be slow
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

12. Use an in-process/in-memory database
For example: HSQLDB
Benefits:
Much faster than a traditional DB: committing transactions, creating schema
Drawbacks:
Different SQL unless using ORM
Some incompatibilities: E.g. time precision
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

13. Committing transactions or not
Strategy
Execute test in a transaction
Rollback transaction at the end
Benefits:
Leaves the database unchanged
Faster
Drawbacks:
Commit time constraints not checked
Services calls that execute in a different transaction can’t see the changes
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

14. ORMUnit – JUnit extension
Simplifies persistence layer tests
Status:
Supports Hibernate and JDO
Currently, part of book’s source code
But will be separated out soon
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

15. Copyright (c) 2006 Chris Richardson. All rights reserved.
Summary
Write lots of tests
Test the metadata when possible
Avoid the DB whenever you can
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.

16. Copyright (c) 2006 Chris Richardson. All rights reserved.
For more information
Buy my book
Stop by Terracotta’s booth (#408)
Send
Visit my website
Book
Blog
This presentation
ORMUnit
1/10/2019
Copyright (c) Chris Richardson. All rights reserved.