Software Testing Day 1: Preliminaries

Software Testing Day 1: Preliminaries
Aditya P. Mathur Purdue University August 12-16 @ Guidant Corporation Minneapolis/St Paul, MN Graduate Assistants: Baskar Sridharan Ramkumar Natarajan Last update: July 23, 2002

Software Testing: Preliminaries
Part I: Preliminaries Learning Objectives What is testing? How does it differ from verification? How and why does testing improve our confidence in program correctness? What is coverage and what role does it play in testing? What are the different types of testing? Software Testing: Preliminaries

Testing: Preliminaries
What is testing? The act of checking if a part or a product performs as expected. Why test? Gain confidence in the correctness of a part or a product. Check if there are any errors in a part or a product. Software Testing: Preliminaries

What to test? During software lifecycle several products are generated. Examples: Requirements document Design document Software subsystems Software system Software Testing: Preliminaries

Test all! Each of these products needs testing. Methods for testing various products are different. Examples: Test a requirements document using scenario construction and simulation Test a design document using simulation. Test a subsystem using functional testing. Software Testing: Preliminaries

What is our focus? We focus on testing programs. Programs may be subsystems or complete systems. These are written in a formal programming language. There is a large collection of techniques and tools to test programs. Software Testing: Preliminaries

Few basic terms Program: A collection of functions, as in C, or a collection of classes as in java. Specification Description of requirements for a program. This might be formal or informal. Software Testing: Preliminaries

Few basic terms-continued
Test case or test input A set of values of input variables of a program. Values of environment variables are also included. Test set Set of test inputs Program execution Execution of a program on a test input. Software Testing: Preliminaries

Few basic terms-continued
Oracle A function that determines whether or not the results of executing a program under test is as per the program’s specifications. Software Testing: Preliminaries

Correctness Let P be a program (say, an integer sort program). Let S denote the specification for P. For sort let S be: Software Testing: Preliminaries

Sample Specification P takes as input an integer N>0 and a sequence of N integers called elements of the sequence. Let K denote any element of this sequence, P sorts the input sequence in descending order and prints the sorted sequence. Software Testing: Preliminaries

Correctness again P is considered correct with respect to a specification S if and only if: For each valid input the output of P is in accordance with the specification S. Software Testing: Preliminaries

Errors, defects, faults Error: A mistake made by a programmer Example: Misunderstood the requirements. Defect/fault: Manifestation of an error in a program. Example: Incorrect code: if (a<b) {foo(a,b);} Correct code: if (a>b) {foo(a,b);} Software Testing: Preliminaries

Failure Incorrect program behavior due to a fault in the program. Failure can be determined only with respect to a set of requirement specifications. A necessary condition for a failure to occur is that execution of the program force the erroneous portion of the program to be executed. What is the sufficiency condition? Software Testing: Preliminaries

Errors and failure Error-revealing inputs cause failure Inputs Program Erroneous outputs indicate failure Outputs Software Testing: Preliminaries

Debugging Suppose that a failure is detected during the testing of P. The process of finding and removing the cause of this failure is known as debugging. The word bug is slang for fault. Testing usually leads to debugging Testing and debugging usually happen in a cycle. Software Testing: Preliminaries

Test-debug cycle Test Yes Failure? No Testing complete? Debug Yes No Done! Software Testing: Preliminaries

Testing and code inspection
Code inspection is a technique whereby the source code is inspected for possible errors. Code inspection is generally considered complementary to testing. Neither is more important than the other! One is not likely to replace testing by code inspection or by verification. Software Testing: Preliminaries

Testing for correctness?
Identify the input domain of P. Execute P against each element of the input domain. For each execution of P, check if P generates the correct output as per its specification S. Software Testing: Preliminaries

What is an input domain ? Input domain of a program P is the set of all valid inputs that P can expect. The size of an input domain is the number of elements in it. An input domain could be finite or infinite. Finite input domains might be very large! Software Testing: Preliminaries

Identifying the input domain
For the sort program: N: size of the sequence, K: each element of the sequence. Example: For N<3, e=3, some sequences in the input domain are: [ ]: An empty sequence (N=0). [0]: A sequence of size 1 (N=1) [2 1]: A sequence of size 2 (N=2). Software Testing: Preliminaries

Size of an input domain Suppose that The size of the input domain is the number of all sequences of size 0, 1, 2, and so on. The size can be computed as: Software Testing: Preliminaries

Testing for correctness? Sorry!
To test for correctness P needs to be executed on all inputs. For our example, it will take several light years to execute a program on all inputs on the most powerful computers of today! Software Testing: Preliminaries

Exhaustive Testing This form of testing is also known as exhaustive testing as we execute P on all elements of the input domain. For most programs exhaustive testing is not feasible. What is the alternative? Software Testing: Preliminaries

Verification Verification for correctness is different from testing for correctness. There are techniques for program verification which we will not discuss. Software Testing: Preliminaries

Partition Testing In this form of testing the input domain is partitioned into a finite number of sub-domains. P is then executed on a few elements of each sub-domain. Let us go back to the sort program. Software Testing: Preliminaries

Sub-domains Suppose that and e=3. The size of the partitions is : We can divide the input domain into three sub-domains as shown. 1 2 3 Software Testing: Preliminaries

Fewer test inputs Now sort can be tested on one element selected from each domain. For example, one set of three inputs is: [ ] Empty sequence from sub-domain 1. [2] Sequence from sub-domain 2. [2 0] Sequence from sub-domain 3. We have thus reduced the number of inputs used for testing from 13 to 3! Software Testing: Preliminaries

Confidence in your program
Confidence is a measure of one’s belief in the correctness of the program. Correctness is not measured in binary terms: a correct or an incorrect program. Instead, it is measured as the probability of correct operation of a program when used in various scenarios. Software Testing: Preliminaries

Measures of confidence
Reliability: Probability that a program will function correctly in a given environment over a certain number of executions. We do not plan to cover Reliability. Test completeness: The extent to which a program has been tested and errors found have been removed. Software Testing: Preliminaries

Example: Increase in Confidence
We consider a non-programming example to illustrate what is meant by “increase in confidence.” Example: A rectangular field has been prepared to certain specifications. One item in the specifications is: “There should be no stones remaining in the field.” Software Testing: Preliminaries

Rectangular Field Search for stones inside the rectangle. W Y L X Software Testing: Preliminaries

Organizing the search We divide the entire field into smaller search rectangles. The length and breadth of each search rectangle is one half that of the smallest stone. Software Testing: Preliminaries

Testing the rectangular field
The field has been prepared and our task is to test it to make sure that it has no stones. How should we organize our search? Software Testing: Preliminaries

Partitioning the field
We divide the entire field into smaller search rectangles. The length and breadth of each search rectangle is one half that of the smallest stone. Software Testing: Preliminaries

Partitioning into search rectangles
Stone 1 2 3 4 5 6 7 8 Width Y 1 2 3 4 5 6 7 Length X Software Testing: Preliminaries

Input domain Input domain is the set of all possible inputs to the search process. In our example this is the set of all points in the field. Thus, the input domain is infinite! To reduce the size of the input domain we partition the field into finite size rectangles. Software Testing: Preliminaries

Rectangle size The length and breadth of each search rectangle is one half that of the smallest stone. This ensures that each stone covers at least one rectangle. (Is this always true?) Software Testing: Preliminaries

Constraints Testing must be completed in less than H hours. Any stone found during testing is removed. Upon completion of testing the probability of finding a stone must be less than p. Software Testing: Preliminaries

Number of search rectangles
Let L: Length of the field W: Width of the field l: Length of the smallest stone w: Width of the smallest stone Size of each rectangle: l/2 x w/2 Number of search rectangles (R)=(L/l)*(W/w)*4 Assume that L/l and W/w are integers. Software Testing: Preliminaries

Time to test Let t be the time to look inside one search rectangle. No rectangle is examined more than once. Let o be the overhead in moving from one search rectangle to another. Total time to search (T)=R*t+(R-1)*o Testing with R rectangles is feasible only if T<H. Software Testing: Preliminaries

Partitioning the input domain
This set consists of all search rectangles (R). Number of partitions of the input domain is finite (=R). However, if T>H then the number of partitions is is too large and scanning each rectangle once is infeasible. What should we do in such a situation? Software Testing: Preliminaries

Option 1: Do a limited search
Of the R search rectangles we examine only r where r is such that (t*r+o*(r-1)) < H. This limited search will satisfy the time constraint. Will it satisfy the probability constraint? Software Testing: Preliminaries

Distribution of stones
To satisfy the probability constraint we must scan enough search rectangles so that the probability of finding a stone, after testing, remains less than p. Let us assume that there are stones remaining after i test cycles. Software Testing: Preliminaries

Distribution of stones
There are search rectangles remaining after i test cycles. Stones are distributed uniformly over the field An estimate of the probability of finding a stone in a randomly selected remaining search rectangle is Software Testing: Preliminaries

Probability constraint
We will stop looking into rectangles if Can we really apply this test method in practice? Software Testing: Preliminaries

Confidence Number of stones in the field is not known in advance. Hence we cannot compute the probability of finding a stone after a certain number of rectangles have been examined. The best we can do is to scan as many rectangles as we can and remove the stones found. Software Testing: Preliminaries

Coverage After a rectangle has been scanned for a stone and any stone found has been removed, we say that the rectangle has been covered. Suppose that r rectangles have been scanned from a total of R. Then we say that the coverage is r/R. Software Testing: Preliminaries

Coverage and confidence
What happens when coverage increases? As coverage increases so does our confidence in a “stone-free” field. In this example, when the coverage reaches 100%, all stones have been found and removed. Can you think of a situation when this might not be true? Software Testing: Preliminaries

Option 2: Reduce number of partitions
If the number of rectangles to scan is too large, we can increase the size of a rectangle. This reduces the number of rectangles. Increasing the size of a rectangle also implies that there might be more than one stone within a rectangle. Software Testing: Preliminaries

Rectangle size As a stone may now be smaller than a rectangle, detecting a stone inside a rectangle is not guaranteed. Despite this fact our confidence in a “stone-free” field increases with coverage. However, when the coverage reaches100% we cannot guarantee a “stone-free” field. Software Testing: Preliminaries

Coverage vs. Confidence
Does not imply that the field is “stone-free”. 1 Confidence Coverage 1(=100%) Software Testing: Preliminaries

Rectangle size p=Probability of detecting a stone inside a rectangle, given that the stone is there. t=time to complete a test. t, p small Rectangle size large Software Testing: Preliminaries

Analogy Field: Program Stone: Error Scan a rectangle:Test program on one input Remove stone: Remove error Partition: Subset of input domain Size of stone: Size of an error Rectangle size: Size of a partition Software Testing: Preliminaries

Analogy…continued Size of an error is the number of inputs in the input domain each of which will cause a failure due to that error. Inputs that cause failure due to Error 1 Inputs that cause failure due to Error 2. Error 1 is larger than Error 2. Input domain Software Testing: Preliminaries

Confidence and probability
Increase in coverage increases our confidence in a “stone-free” field. It might not increase the probability that the field is “stone-free”. Important: Increase in confidence is NOT justified if detected stones are not guaranteed to be removed! Software Testing: Preliminaries

Types of testing Basis for classification Source of clues for test input construction Object under test All of these methods can be applied here. Software Testing: Preliminaries

Testing: based on source of test inputs
Functional testing/specification testing/black-box testing/conformance testing: Clues for test input generation come from requirements. White-box testing/coverage testing/code-based testing Clues come from program text. Software Testing: Preliminaries

Stress testing Clues come from “load” requirements. For example, a telephone system must be able to handle 1000 calls over any 1-minute interval. What happens when the system is loaded or overloaded? Software Testing: Preliminaries

Performance testing Clues come from performance requirements. For example, each call must be processed in less than 5 seconds. Does the system process each call in less than 5 seconds? Fault- or error- based testing Clues come from the faults that are injected into the program text or are hypothesized to be in the program. Software Testing: Preliminaries

Random testing Clues come from requirements. Test are generated randomly using these clues. Robustness testing Clues come from requirements. The goal is to test a program under scenarios not stipulated in the requirements. Software Testing: Preliminaries

OO testing Clues come from the requirements and the design of an OO-program. Protocol testing Clues come from the specification of a protocol. As, for example, when testing for a communication protocol. Software Testing: Preliminaries

Testing: based on item under test
Unit testing Testing of a program unit. A unit is the smallest testable piece of a program. One or more units form a subsystem. Subsystem testing Testing of a subsystem. A subsystem is a collection of units that cooperate to provide a part of system functionality Software Testing: Preliminaries

Integration testing Testing of subsystems that are being integrated to form a larger subsystem or a complete system. System testing Testing of a complete system. Software Testing: Preliminaries

Regression testing Test a subsystem or a system on a subset of the set of existing test inputs to check if it continues to function correctly after changes have been made to an older version. And the list goes on and on! Software Testing: Preliminaries

Test input construction and objects under test
Requirements Source of clues for test inputs Code unit subsystem system Test object Software Testing: Preliminaries

Summary: Terms Testing and debugging Specification Correctness Input domain Exhaustive testing Confidence Software Testing: Preliminaries

Summary: Terms [continued] Reliability Coverage Error, defect, fault, failure Debugging, test-debug cycle Types of testing, basis for classification Software Testing: Preliminaries

Summary: Questions What is the effect of reducing the partition size on the probability of finding errors? How does coverage effect our confidence in program correctness? Does 100% coverage imply that a program is fault-free? What decides the type of testing? Software Testing: Preliminaries

Software Testing Day 1: Preliminaries

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