Software Testing

Software Testing

Software Life Cycle • Sommerville , 1992: Development efforts are typically distributed as follows: Specifications/Design30% - 40% Implementation15% - 30% Testing 25% - 50%

Remarks by Bill Gates17th Annual ACM Conference on Object-Oriented Programming, Seattle, Washington, November 8, 2002 • “… When you look at a big commercial software company like Microsoft, there's actually as much testing that goes in as development. We have as many testers as we have developers. Testers basically test all the time, and developers basically are involved in the testing process about half the time… • … We've probably changed the industry we're in. We're not in the software industry; we're in the testing industry, and writing the software is the thing that keeps us busy doing all that testing.”

Remarks by Bill Gates (cont’d) • “…The test cases are unbelievably expensive; in fact, there's more lines of code in the test harness than there is in the program itself. Often that's a ratio of about three to one.” • “… Well, one of the interesting questions is, when you change a program, … what portion of these test cases do you need to run?“

Remarks by Bill Gates (cont’d) • “We also went back and say, OK, what is the state-of-the-art in terms of being able to prove programs, prove that a program behaves in a certain way? …And although a full general solution to that is in some ways unachievable, for many very interesting properties this idea of proof has come a long way in helping us quite substantially just in the last year… • “We use model-checking… You describe the constraints, such as ‘nobody should acquire the lock if they've already acquired it’ … then it's trying to go through to determine is there some path through the program that violates the constraints. … The initial domain we applied this in was in device drivers… “

The V-model of development Implementation and unit testing

From V to Y: automatic code generation ... Specification ... ... Detailed design ... Automatic Code-generation Implementation Unit-test

Some popular testing categories Black box / white box Static / dynamic

Specification-based testing Reflects true intention of testing Does not propagate errors from previous versions Regression testing Does not need a specification Easy to implement Finds subtle errors Testing methodologies

Black Box Testing(Behavioral testing) • How shall we check the I/O relation ? • Manually (specification-based) • Table of expected results ( a simple version of non-temporal specification-based) • Compare results to previous version (Regression testing) Input Output System under test

Black Box Testing (Behavioral testing) Output Input • Testing Input-Outputrelationships only • Pros • This is what the product is about. • Implementation independent. • Cons • For complicated products it is hard to identify erroneous output. • It is hard to estimate whether the product is error-free. • Practically: Choosing input with high probability of error detectionis very difficult (e.g. division of two numbers).

White Box Testing (Operational Testing) • Testing how input becomes output(including algorithms) • Pros • Easier to detect errors. • Enables to find better tests (direct the tests) • The only way to check coverage. • Cons • Implementation weaknesses are not necessarily those of the product. • Code is not always available

Static and Dynamic Testing • Dynamic testing (Run your program) • Predefined tests • Good for Regression Testing (comparing an old version against a new one) • Testing the product under extreme conditions (stree-testing) • Random tests • “real life” tests • Static testing (Inspect your code) • Code analyzers (e.g., tools like lint and purify) • Inspection (code review) • Proofs (by tools, or by mathematical arguments): “formal methods” (incl. Model-checking).

Special Testing Methods • . • Stress Testing A product that will work under heavy load (e.g, on-line banking system) should be tested under increasing load - much heavier than expected.

Static Testing • Code analysis • Unreachable code • Objects declared and never used • Parameters type/number mismatch • Variable used before initialization • Variable is assigned to twice, without using the first value • Function results not used • Possible array bound violations

Static Testing • Code inspection • Self - The default choice. • Subtle errors and micro-flaws may be overlooked. • Wrong conceptions propagate to review… • Code reviewby others -Very efficient !

One more quote… • Dijkstra: “Testing can only prove the existence of bugs, not their absence…”

… So why not try to prove correctness? • In general – it is undecidable, i.e. can’t be done. • In most cases it is possible, but with manual assistance – the same way we would prove a math theorem. • In some cases properties of software can be proved automatically. • Chances for errors increase with length of text • Write short code (e.g, divide into more functions). • Provide short proofs for correctness (even if they are informal).

Estimate how clean is your software • Error Implantation (For measuring the effectiveness of testing) • Introduce errors. • See how many of them are detected. • This gives us an “educated guess” about testing quality.

Estimate how much of the software’s behavior is covered • Coverage is a mean to estimate how rigorous is the testing effort • We can use coverage information in order to guide the process of test generation (some times even automatically)

Statement CoverageExample 1 int a, b, sum; int list1[10] = {0,1,2,3,4,5,6,7,8,9}; int list2[10] = {9,8,7,6,5,4,3,2,1,0}; cin >> a >> b; if (a >= 0 && a <= 9) sum = list1[a]; if (b >= 0 && b <= 9) sum = sum + list2[b]; cout << sum << "\n";

Statement CoverageExample 1 if (a >= 0 && a <= 9) sum = list1[a]; if (b >= 0 && b <= 9) sum = sum + list2[b]; • Statement coverage may be achieved by __ test case(s):

Statement CoverageExample 1 if (a >= 0 && a <= 9) sum = list1[a]; if (b >= 0 && b <= 9) sum = sum + list2[b]; • But statement coverage may not cater for all conditions... • ... such as when a and b are beyond the array size.

Branch CoverageSame Example 1 if (a >= 0 && a <= 9) sum = list1[a]; if (b >= 0 && b <= 9) sum = sum + list2[b]; • Branch coverage may be achieved by __ test cases.

Branch coverage: Example switch (x){ case 1: x = 1; break; case 2: switch (y){ case 1: x = 3; break; case 2: x = 2; break; otherwise: x = 1; } otherwise: 4;} • branch coverage may be achieved by __ test cases

Path CoverageSame Example 2 if (a >= 0 && a <= 9) sum = list1[a]; else sum = 0; if (b >= 0 && b <= 9) sum = sum + list2[b]; else sum = 0; • Path coverage may be achieved by __ test cases:

Subsumption Relationships Path coverage subsumesBranch coverage subsumesStatement coverage • But can we always demand path coverage?

Branch CoverageExample 3 if (a >= 0 && a <= 9) sum = list1[a]; else sum = 0; if (b >= 0 && b <= 9) sum = sum + list2[b]; else sum = 0; ... if (z >= 0 && z <= 9) sum = sum + list26[b]; else sum = 0; • Branch coverage may be achieved by __ test cases

Path CoverageSame Example 3 if (a >= 0 && a <= 9) sum = list1[a]; else sum = 0; if (b >= 0 && b <= 9) sum = sum + list2[b]; else sum = 0; ... if (z >= 0 && z <= 9) sum = sum + list26[b]; else sum = 0; • Path coverage may be achieved by __ test cases

Statement CoverageExample 4 sum = 0; while (a >= 0 && a <= 9) { sum = list1[a]; a = a + 1; }; if (b >= 0 && b <= 9) sum = list2[b]; else sum = 0; • Statement coverage may be achieved by __ test cases:

Branch CoverageSame Example 4 sum = 0; while (a >= 0 && a <= 9) { sum = list1[a]; a = a + 1; }; if (b >= 0 && b <= 9) sum = list2[b]; else sum = 0; • Branch coverage may be achieved by __ test cases:

Loop coverage • Skip the loop entirely • Only 1 pass through the loop • 2 passes through the loop • n–1, n and n+1 passes through the loop, where n is the maximum number of allowable passes

Loop CoverageSame Example 4 sum = 0; while (a >= 0 && a <= 9) { sum = list1[a]; a = a + 1; }; if (b >= 0&& b <= 9) sum = list2[b]; else sum = 0; • Loop coverage may be achieved by __ test cases

Path CoverageSame Example 4 sum = 0; while (a >= 0 && a <= 9) { sum = list1[a]; a = a + 1; }; if (b >= 0 && b <= 9) sum = list2[b]; else sum = 0; • Path coverage may be achieved by __ test cases

Subsumption Relationships Path coverage subsumesBranch coverage subsumesStatement coverage  Path coverage subsumes Loop coverage But can we always demand path coverage?

Path CoverageExample 5 sum = 0; while (a >= 0 && a <= 9) { sum = list1[a]; a = a + 1; }; while (b >= 0 && b <= 9) { sum = list2[a]; b = b + 1; }; ... while (z >= 0 && z <= 9) { sum = list26[z]; z = z + 1; }; • Path coverage may be achieved by __ test cases

Path Coverage is not EverythingExample 1 z = x + y; Path coverage may be achieved by 1 test case x = 8, y = 0 Cannot detect z = x - y; x = 2, y = 2 Cannot detect z = x * y; x = 8, y = 9 Cannot detect z = 8 + y; Cannot detect z = x + 9; We need 2 test cases: x = 8, y = 9 x = 29, y = 18.

Path Coverage is not EverythingExample 2 int a[10]; if (b > 0) a[b] = 1; else … Same path with b = 5 and b = 12 behave differently

Condition coverageExample if (b1 ||(b2 && b3)) a = 1; else … Every sub-expression in a predicate should be evaluated to TRUE and FALSE • Sub-expression coverage may be achieved by __ test cases

Multiple condition coverageExample if (b1 ||(b2 && b3)) a = 1; else … Every Boolean combination of sub-expressions in a predicate should be evaluated to TRUE and FALSE • Multiple condition coverage may be achieved by __ test cases

Condition/Branch coverage (MC / DC)(Modified Condition/Decision Coverage) if (!b1 || b2) a = 1; else … Modified – due to some constructs not present in C / C++. Decision coverage = Branch coverage Union of Condition coverage and Branch coverage This is an industry standard, introduced by Boeing • MC/DC coverage may be achieved by __ test cases

Specification-based testing • We will see an example of a system for specification-based testing of real-time applications. • It is a Run-time verification tool. • The testing system is called “Logic Assurance” • It monitors the specification, and can also intervene in the execution of the program.

Overview Monitoring control Logic Report state Assurance Event Reporting System Under Development ReportState Environment control Optional =

The user should: 1. Specify rules: • Formalize parts of the specification by writing rules in the specification Language. • The rules should refer to events, the System Under Development (SUD)'s variables, external data etc..

A typical specification language: The LA Language (LAL)Derived from Temporal Logic and C, LAL enables specification of: • Event order. • Relative frequency ("fairness"). • Timing demands. • Logical and mathematical operators. • More...

Examples(1/4): 1. Using event names, time directives and messages: OPEN_DOOR follows CLOSE_DOOR after not more than 10 sec ?: message("Open door is late");

...Examples(2/4) 2. Logical operators and functions: when time>20: time([CLOSE_DOOR])> time([OPEN_DOOR])+10?: message("CLOSE_DOOR is early");

...Examples(3/4) 3. User-defined functions are used to enhance the language and enable external control: if JOB_DONE(10) then HEAT(3,5) < 30?: REDUCE_HEAT(5);

...Examples(4/4) 4. Locators are used to scan the log and retrieve event index: [2nd SEND s.t. Time>=10, packet=5] > 0 ?: REDUCE_HEAT(5);

2. Report events: • From inside the SUD by using the LA Report Facility. • From outside the SUD by using black-box techniques (e.g. OS events) • From the environment (Sensors, etc.)

Software Testing