This document discusses testing elementary components in JUnit, including testing equals methods, methods that return nothing, constructors, getters, setters, interfaces, exceptions, collections, large objects, and objects that instantiate other objects. It provides examples and recommendations for each, such as comparing the result of a getter to an expected value, analyzing the side effects of methods that return nothing, and using a "spy" subclass to observe the behavior of a setter. The document is divided into sections for each of these elementary testing scenarios.

1. JUnit Recipes
- Elementary tests
Zheng-Wen Shen
2007/10/25
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2. Brief contents
 Part 1: The Building Blocks
1. Fundamentals
2. Elementary tests
3. Organizing and building JUnit tests
4. Managing test suites
5. Working with test data
6. Running JUnit tests
7. Reporting JUnit results
8. Troubleshooting JUnit
 Part 2: Testing J2EE
 Part 3: More JUnit Techniques
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3. The Building Blocks
Elementary tests
1. Test your equals methods
2. Test a method that returns nothing
3. Test a constructor
4. Test a getter
5. Test a setter
6. Test an interface
7. Test throwing the right exception
8. Let collections compare themselves
9. Test a big object for equality
10.Test an object that instantiates other objects
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4. The Building Blocks
Elementary tests
1. Test your equals methods
2. Test a method that returns nothing
3. Test a constructor
4. Test a getter
5. Test a setter
6. Test an interface
7. Test throwing the right exception
8. Let collections compare themselves
9. Test a big object for equality
10.Test an object that instantiates other objects
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5. 1. Test your equals methods (1/3)
Test the implementation of equals()
 Value Object: represents a value
 String, Integer, Double, Money, Timestamp,
etc.
Money a= new Money(100,0);
Money b= new Money(100,0); a
Money c= new Money(50,0); b
Money d= new Money(50,0); 100, 0
100, 0
a.equals( b ); // true
a.equals( c ); // false
c.equals( d ); // true c
c.equals( a ); // false
50, 0 d
50, 0
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6. 1. Test your equals methods (2/3)
Test the implementation of equals()
 The contract of equals()
 Equivalence relations (RST)
• Reflexive property
• Symmetric property
• Transitive property
 Consistent
 No object equals null
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7. 1. Test your equals methods (3/3)
Test the implementation of equals()
equal to a
not equal to a
“looks equal”
JUnit utility
RST, consistent, no object is equal null…
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8. 2. Test a method that returns nothing
(1/3)
 “How do I test a method that return void?”
 If a method returns no value, it must have
some observable side effect!
xyz obj = new xyz(); xyz object state
obj.change(); // transit to A
obj.change(); // transit to B Start A
obj.change(); // transit to C
obj.change(); // transit to D
B C
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9. 2. Test a method that returns nothing
(2/3)
 To test the Collection.add(Object)
1. Create an empty collection
2. The collection should not contain the item in question
3. Add the item in question
4. Now the collection should contain the item in question
1
2
return nothing 3
4
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10. 2. Test a method that returns nothing
(3/3)
 We are testing behavior, and not methods.
 If code does the wrong thing but no test
fails, does it have as defect?

NOTE The tests are the specification!!
 We describe what our code does by providing
the tests our code passes.
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11. 3. Test a constructor
 Uses exposed internal state
 Observable side effect
 Pitfalls
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12. 4. Test a getter (1/3)
Which tests are needed and which are not
 Do not test methods that too simple to
break!!
too simple
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13. 4. Test a getter (2/3)
Which tests are needed and which are not
 Compare that result with an expected
value
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14. 4. Test a getter (3/3)
Which tests are needed and which are not
An alternative implementation…
Too simple to break
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15. 5. Test a setter (1/3)
Should I test my set methods?
 Basic set methods are too simple to break
 Effective way to test if you have to:
pattern 1
2
3
4
1. Name the test method appropriately
2. Create an instance of your bean class
3. If newPropertyValue is a complex property, then initialize
newPropertyValue.
4. If property is a more complex object than string, then you need
to ensure that equals() is appropriately implemented
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16. 5. Test a setter (2/3)
Should I test my set methods?
If there are no get methods…
Command
Analyze the side effect
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17. 5. Test a setter (3/3)
Should I test my set methods?
BankTransferAction action = new BankTransferAction();
action.setSourceAccountId("source");
action.setTargetAccountId("target");
action.setAmount(Money.dollars(100));
Bank
“Spy”
Subclass
Of Bank
(Spy)
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18. The Building Blocks
Elementary tests
1. Test your equals methods
2. Test a method that returns nothing
3. Test a constructor
4. Test a getter
5. Test a setter to be continue…
6. Test an interface
7. Test throwing the right exception
8. Let collections compare themselves
9. Test a big object for equality
10.Test an object that instantiates other objects
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