1. Testing Data Structures
CSE 373
Tao Xie
Dept. of Computer Science and Engineering
University of Washington, Seattle

2. Objectives Master practical testing techniques
use similar techniques to test students' own code at hand
handle programming interview questions related to testing
Master systematic testing techniques
apply both black-box and white-box testing techniques
effectively use the JUnit framework and code-coverage tool

3. = Testing Setup ? Test inputs Program Expected Outputs Outputs Test 1
void test1() {
BST t = new BST ();
t.insert(2); t.size();
t.remove(2); t.contain(2); }
public class BST {
void insert(int v) { … }
void remove(int v) { … }
... }
t.size(): 1
t.contain(2): false
t.size(): 1
t.contain(2): false

4. How is it different to test LinkedList than Anagram?
Testing LinkedList
Test a LinkedList’s get(int X), which returns the element at the specified position in this list.
Testing Anagram
Test a method which checks whether two words are anagrams of each other
Test a method which checks to see if a word has any anagrams in a dictionary of words

5. How is it different to test LinkedList than Anagram?
Testing LinkedList
Test a LinkedList’s get(int X), which returns the element at the specified position in this list.
A data structure has object states
Input =
receiver-object +
method arguments
Method Execution
Output =
receiver-object +
method return

6. How is it different to test LinkedList than Anagram?
Testing LinkedList
Test a LinkedList’s get(int X), which returns the element at the specified position in this list.
A data structure has object states
Implicit input for a method besides arguments
How to prepare object states? e.g. a LinkedList with size 5
What object states to prepare?
Implicit output for a method besides return
How to check object states?

7. Classic Unit Test Construction
public void testLinkedListXXX {
Construct the object state under test (OUT)
Optionally save the state of the OUT
Call the method under test (MUT)
if an exception was generated
Test for unhandled exceptions
else
Assertions on the return, OUT, and arguments }

8. LinkedList add Example
How to know we get an expected new LinkedList object after calling add(5) on a LinkedList object (containing 1 and 5)?
public testLinkedListAdd3 () {
LinkedList s = new LinkedList();
s.add(1);
s.add(5);//s is now prepared as OUT
s.add(5);//MUT
assertTrue(?????);
... }
Backup/regenerate OUT
LinedList b = s.clone(); OR
LinedList b= new LinkedList();
b.add(1);
b.add(5);

9. Asserting Object States
How to know we get an expected new LinkedList object after calling add(5) on a LinkedList object (containing 1 and 5)?
Invoke other non-void-return methods (observers) on the new object, e.g., assertTrue(s.contains(5)), assertTrue(s.getLast()==5), assertTrue(s.size()==3).
Invoke toString() on the new object, e.g., assertTrue(s.toString().equals(“1,5,5”))
Invoke equals() on the new object, e.g., assertTrue(!s.equals(…)). When we call s.add(5) and s.removeLast(5) on an object state S, we want to check the new object is equal to S. Need backup/clone S or regenerate S

10. = Testing Techniques Black-box testing White-box testing ?
Equivalence Partitioning Testing
Boundary Value Testing
White-box testing
Statement coverage
program
test inputs
Outputs
Expected Outputs = ?
void test99() {
BST t = new BST ();
t.insert(2); t.size(); }
public class BST {
void insert(int v) { … }
void remove(int v) { … }
... }
t.size(): 1
t.contain(2): false
t.size(): 1
t.contain(2): false

11. From Diane Horton’s handout
Example
Consider a method findMax that is supposed to find the max element in a LinkedList:
We test the method on the following inputs and observe the outputs as shown:
Can we claim that the method is correct ?
From Diane Horton’s handout

12. From Diane Horton’s handout
Example
It seems these 10 test cases are good enough; but in fact, they are not well chosen
We can easily construct a method that passes these then cases but fails in:
A very short list (i.e., of length 1, 2, or 3)
An empty list (i.e., of length 0) In fact, easy to forget to specify the method’s behavior for this type of “boundary” case
A list where the max elem is the first or last element.
A list where the max elem is negative
In fact, all 10 tests cover essentially the same situation
A list of moderate length, all positive integers, the max elem is somewhere in the middle
From Diane Horton’s handout

13. Equivalence Partitioning
Input domain is usually too large for exhaustive testing.
Partition input domain into a finite number of sub-domains for the selection of test inputs.
Each sub-domain is known as an equivalence class and serves as a source of at least one test input.
Input domain
partitioned into four
sub-domains. 1 2 3 4
Input domain
Too many
test inputs.
Four test inputs, one
selected from each sub-domain.

14. Which index X shall we test?
How to partition?
Inputs to a program provide clues to partitioning.
Example: given a LinkedList with size 10, get(int X) returns the element at the specified position in this list.
Prohibitively large input domain: X can assume a large number of values.
Which index X shall we test?

15. How to partition?
Example: given a LinkedList with size 10, get(int X) returns the element at the specified position in this list.
We expect LinkedList to
behave the same way for all X<0
behave the same way for all X>9
behave the similar way for all 0<=X<=9
Partition the input domain of P into three sub-domains.

16. How to partition?
One test case:
X=-3
Equivalence class
X>9
Another test case:
X=15
X<0
Another test case:
X=5
0<=X<=9
All test inputs in the X<0 sub-domain are considered equivalent. The assumption is that if one test input in this sub-domain reveals an error in the program, so will the others.
This is true of the test inputs in the X>9 sub-domain or the 0<=X<=9 sub-domain too.
Then we selected just enough tests to cover each partition.
The rationale of our new approach for defining redundant tests is to focus on each method execution individually and consider that it is unnecessary to …
In other words, we assume the code under test is single-threaded. To support testing multithreading programs, we need to focus on execution entities with a finer granularity than method executions. We leave this to our future work.

17. Guideline for Partitioning
Input condition specifies a range: create one for the valid case and two for the invalid cases.
e.g., for a<=X<=b the classes are
a<=X<=b (valid case)
X<a and X>b (the invalid cases)
Input condition specifies a value: create one for the valid value and two for incorrect values (below and above the valid value).
This may not be possible for certain data types, e.g., for boolean.
Input condition specifies a member of a set: create one for the valid value and one for the invalid (not in the set) value.
e.g., contains(Object o)

18. Boundary Value Testing
Errors tend to be concentrated at edges of input domain – look for boundary values as test inputs
One test case:
X=-3
Equivalence class
X>9
Another test case:
X=15
X<0
Another test case:
X=5
0<=X<=9
Equivalence class
X=0 and X=9 are boundaries. Inputs to the program might lie on the boundary or on either side of the boundary.
Lie on boundary: 0, 9
Lie on valid side of the boundary: 1, 8
Lie on Invalid boundary cases: -1, 10

19. Testing Arbitrary LinkedList
Example: given a LinkedList with size 10, get(int X) returns the element at the specified position in this list.
Input: X
Input condition ?
0<=X<=9

20. Testing Arbitrary LinkedList
Example: given a LinkedList with size 10, get(int X) returns the element at the specified position in this list.
Input: X
Inputs: X, S
Input condition
Input conditions
0<=X<=9
s.size()>=0
0<=X<= s.size()-1
What tests to generate?

21. Another example
Example: given a LinkedList, contains(Object e) returns true if this list contains the specified element.
Inputs: e, S
Input conditions ?

22. Adapted from Norman Fenton’s slide
Another example
Example: given a LinkedList, contains(Object e) returns true if this list contains the specified element.
Inputs: e, S
LinkedList s of size n
Input conditions
Input condition
s.size()>=0
e not in s e in s (e’s position)
Adapted from Norman Fenton’s slide

23. How many tests shall be generated?
Example: given a LinkedList, contains(Object e) returns true if this list contains the specified element.
Inputs: e, S
LinkedList s of size n
Input conditions
Input condition
s.size()>=0
e not in s e in s (e’s position)
Adapted from Norman Fenton’s slide

24. How many tests shall be generated?
Example: given a LinkedList, remove(Object e) returns true if this list contains the specified element.
Inputs: e, S
LinkedList s of size n
Input conditions
Input condition
s.size()>=0
e not in s e in s (e’s position)
Adapted from Norman Fenton’s slide

25. findMax example revisited
Consider a method findMax that is supposed to find the max element in a LinkedList
We can easily construct a method that passes these then cases but fails in:
A very short list (i.e., of length 1, 2, or 3)
An empty list (i.e., of length 0) In fact, easy to forget to specify the method’s behavior for this type of “boundary” case
A list where the max elem is the first or last element.
A list where the max elem is negative
How can we generate these tests using the techniques we just learned?
what test conditions?  what tests?

26. findMax example revisited
Consider a method findMax that is supposed to find the max element in a LinkedList
We can easily construct a method that passes these then cases but fails in:
A very short list (i.e., of length 1, 2, or 3)
An empty list (i.e., of length 0) In fact, easy to forget to specify the method’s behavior for this type of “boundary” case
A list where the max elem is the first or last element.
A list where the max elem is negative
Input: s
Input conditions: s.size()>=0, 0<=max’s position<s.size() MIN < max’s value < MAX

27. White-Box Testing
Determining test cases from a knowledge of the internal logic of the software
Four main types of white-box testing
Statement Testing
Loop Testing
Path Testing
Branch Testing

28. White-Box Testing Statement Testing: Test single statements
Loop Testing:
Cause execution of the loop to be skipped completely. (Exception: Repeat loops)
Loop to be executed exactly once
Loop to be executed more than once
Path testing:
Make sure all paths in the program are executed
Branch Testing (Conditional Testing): Make sure that each possible outcome from a condition is tested at least once
if (i == true)
System.out.println("YES");
else
System.out.println("NO");
Test cases: 1) i = true; 2) i = false

29. White-Box Testing Statement Testing: Test single statements
Loop Testing:
Cause execution of the loop to be skipped completely. (Exception: Repeat loops)
Loop to be executed exactly once
Loop to be executed more than once
Path testing:
Make sure all paths in the program are executed
Branch Testing (Conditional Testing): Make sure that each possible outcome from a condition is tested at least once
if (i == true)
System.out.println("YES");
System.out.println("OK");
Test cases: 1) i = true; 2) i = false

30. JCoverage tool Measure statement coverage Demo
Know which statements haven’t been exercised
Then you can try to generate tests to exercise them
A challenging problem though for complex programs
Demo

31. Both black-box and white-box testing are needed
From Norman Fenton’s slide