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Some Testing Techniques
(enhanced 6 + 4)
Course Software Testing & Verification
2013/14
Wishnu Prasetya
Plan
•
•
•
•
Unit testing
 tool
Mocking (Sec. 6.2.1)  enhanced
Black box testing  Input Partitioning (Ch 4).
Regression (6.1)  enhanced
2
Unit Testing
• Making sure that the units are correct.
• Insufficient unit testing can be costly:
debugging an error at the system-test level is
much more costly than at the unit level (some
reports suggest more than 10x).
• Don’t confuse the concept of “unit testing”
and “unit testing tool”; the later can often also
be used to facilitate integration and system
testing.
3
But what is a “unit” ?
• In principle, you decide. “Units” are just something
you can compose to build something bigger.
Possibilities: function, method, or class.
• But be aware that different types of units may have
types of interactions and complexity, thus requiring
different testing approach
– a function’s behavior depends only on its parameters; does
not do any side effect.
– procedure depends-on/affects params and global
variables
– method: static vars, params, instance vars
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– class: is a collection of interacting methods
Unit testing in C#
• You need at least Visual Studio Professional; and for
code coverage feedback you need at least Premium.
• Check these tutorials/docs (Visual Studio 2010):
–
–
–
–
Walkthrough: Creating and Running Unit Tests
Walkthrough: Run Tests and View Code Coverage
Walkthrough: Using the Command-line Test Utility
API Reference for Testing Tools for Visual Studio, in
particular Microsoft.VisualStudio.TestTools.UnitTesting,
containg classes like
• Assert, CollectionAssert, ...
• In this lecture we will just go through the concepts
5
The structure of a “test project”
class Thermometer
private double val
private double scale
private double offset
public Thermometer(double s, double o)
public double value()
public double warmUp(double v)
public double coolDown(double v)
A test project is a just a project in your
solution that contains your test-classes.
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The structure of a “test project”
• A solution may contain multiple projects; it may thus
contain multiple test projects.
• A test project is used to group related test classes.
• You decide what “related” means; e.g. you may want
to put all test-cases for the class Thermometer in its
own test project.
• A test class is used to group related test method.
• A test method does the actual testing work. It may
encode a single test-case, or multiple test-cases. You
decide.
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Test Class and Test Method
[TestClass()]
public class ThermometerTest {
private TestContext testContextInstance;
//[ClassInitialize()]
//public static void MyClassInitialize(...) ...
//[ClassCleanup()]
//public static void MyClassCleanup() ...
//[TestInitialize()]
//public void MyTestInitialize() ...
//[TestCleanup()]
//public void MyTestCleanup() ...
[TestMethod()]
public void valueTest1() ...
[TestMethod()]
public void valueTest2() ....
public void valueTest1() {
target = new Thermometer(1,0);
double expected = - 273.15 ;
double actual = target.value();
Assert.AreEqual(expected, actual);
}
Be careful when comparing floating
numbers, you may have to take
imprecision into account, e.g. use this
instead:
AreEqual(expected,actual,delta,”...”)
}
8
Positive and Negative Test
• Positive test: test the program on its normal
parameters’ range.
• But can we afford to assume that the program
is always called in its normal range?
Else do Negative test: test that the program
beyond its normal range.
• E.g. when unit testing a method, to test if it
throws the right kind of exceptions.
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Test Oracle
some patterns  will return later
public void valueTest1() {
target = new Thermometer(1,273.15);
double expected = - 273.15 ;
double actual = target.value();
Assert.AreEqual(expected, actual);
}
An oracle specifies your
expectation on the program’s
responses.
• Full: Assert.IsTrue( T == -273.15)
• Partial: Assert.IsTrue( T >= -273.15)
• Property-based : Assert.isTrue(safe(T))
More costly to maintain,
e.g. if you change the
intended behavior of the
program.
Usually partial, but allow re-use the predicate “safe” in
other test-cases.
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Discussion: propose test cases
in particular the oracles...
reverse(a) {
N = a.length
if (N  1) return
for (int i=0; i< N/2 ; i++)
swap(a,i, N-1-i)
}
incomeTax(i) {
if (i18218) return 0.023 * i
t = 419
if (i32738)
return t + 0.138 * (i – 18218)
t += 1568
if (i54367)
return t + 0.42 * (i – 32738)
}
Property-based testing fits nicely for reverse, but not for incomeTax; for the latter we’ll have
to fall back to conrete-value oracles, which unfortunately tend to be more costly to
maintain.
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Discussion: the Oracle Problem (6.5)
• Every test-case needs an oracle; how to construct it!?
 always a big problem!
• Using concrete values as oracles is often powerful,
but potentially expensive to maintain.
• Using “properties” on the other hand has the
problem that often it is hard to write a complete yet
simple property capturing correctness. E.g. how to
express an oracle for a sorting function?
• Alternatively we can fall back to redundancy-based
testing.
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Inspecting Test Result
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Inspecting Coverage
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Finding the source of an error: use a
debugger!
•
•
•
Add break points; execution is stopped at
every BP.
You can proceed to the next BP, or execute
one step at a time: step-into, step-over,
step-out.
VisualStudio uses IntelliTrace  logging 
you can even inspect previous BPs.
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The Debug class
• Debug.Print(“therm. created”)
• Debug.Assert(t.scale() > 0) to check for
properties that should hold in your program.
• Will be removed if you build with debug off
(for release).
• Check the doc of System.Diagnostics.Debug
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(Unit) Testing a class
• Many classes have methods that interact with
each other (e.g. as in Stack). How to test these
interactions?
• How to specify and test these interactions?
Options:
– class invariant
– Abstract Data Type (ADT)
– Finite State Machine (FSM)
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Specifying with class invariant
• Regardless the interaction with other
methods, each method of a class C has to
keep the state of its target object consistent.
• Express this with a class invariant, e.g.
– this.T >= -273.15
– this.saldo >= 0
– forall x in persons, typeOf(x) is Employee
• Class invariant cannot express a constraint
over the interaction itself.
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Formulate and test the class invariant
Stack<T>
private Object[] content
private int top
public Stack()
push(T x)
T pop()
bool classinv() {
return
0top
&& top<content.length
}
}
Example test-cases, check
class-inv after :
1. call to the constructor
2. constructor ; push(x)
3. constructor ; push(x) ; push()
4. constructor ; push(x) ; pop()
5. some random sequence of
push and pop
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Specifying a class as an ADT
• An Abstract Data Type (ADT) is a model of a
(stateful) data structure. The data structure is
modeled abstractly by only describing a set of
operations (without exposing the actual
state).
• The semantic is described in terms of “logical
properties” (also called the ADT’s axioms) over
those operations.
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Example : stack
Stack<T>
bool isEmpty()
push(T x)
T pop()
Stack axioms :
•For all x,s :
s.push(x) ; y = s.pop ;
assert (y==x )
• For all x and s :
s.push(x) ;
assert ( s.isEmpty())
Depending of the offered
operations, it may be hard/not
possible to get a complete
axiomatization.
• For all x and s.isEmpty() :
s.push(x) ; s.pop
assert (s.isEmpty())
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Test each ADT’s axiom
For all x,s :
s.push(x) ; y = s.pop ;
assert (y==x )
For example, three test cases :
1. empty s
2. non-empty s
3. s already contains x
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Specifying a class with a finite state machine (FSM)
(2.5.1, 2.5.2)
File:
open()
write()
close()
FSM can also come from your
UML models.
• good when the sequence with which the methods of the class is
called matters
• For example, test that after every valid sequence the class invariant
hold.
• relevant concepts to apply: node coverage, edge coverage, edge23
pair coverage.
In a larger project....
• You want to test your class Heater ; it uses
Thermometer which is not ready yet!
• We can opt to use a mock Thermometer. A mock of a
program P:
– has the same interface as P
– only implement a very small subset of P’s behavior
– fully under your control
• Analogously we have the concept of mock object.
• Make mocks yourself e.g. exploiting inheritance, or use
a mocking tool.
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Mocking with Moq
class Heater
double limit
bool active
public check() {
if (thermometer.value() >= limit)
active = false
}
thermometer
interface IThermometer
double value()
double warmUp(double v)
test1() {
Heater heater = new Heater()
var mock = new Mock<IThermometer>()
mock.Setup(t => t.value()).Returns(-275.15)
heater.thermometer = mock.object
heater.limit = 303.0
heater.check()
Assert.IsFalse(heater.active)
}
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Mocking with Moq
(google it for more info!)
var mock = new Mock<IThermometer>()
mock.Setup(t => t.value()).Returns(303.00001)
mock.Setup(t => t.warmUp(0)).Returns(0)
mock.Setup(t => t.warmUp(It.IsInRange <double>(-10, 10, Range.Inclusive))
.Returns(0)
mock.Setup(t => t.warmUp (It.IsAny<double>()))
.Returns((double s) => s + 273.15)
Many more mock-functionalities in Moq; but in general mocking can be tedious.
E.g. what to do when your Heater wants to call warmUp in an iteration?
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Beyond unit testing, what if we don’t
have access to the source code ?
• Or you deliberately want to abstract away
• Or, you do have access, but you don’t have a
tool to instrument the code
• (Def 1.26) White box testing : common at the
unit-testing level
• (Def 1.25) Black box testing: common at the
system-testing level. Approaches :
– Model-based testing
– Partition-based testing
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Model-based testing
TextEditor:
new(fname)
type(c)
save()
• We already seen that  use an FSM as a model of
the system you test
• Such an FSM specifies :
– sequences which should be valid and invalid
– these tell you which sequences to test
– furthermore, coverage can be defined over the FSM
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Model-based testing
size() = 0
TextEditor:
new(...)
save()
type(c)
type(c)
size() > 0
• Predicates can be defined on the FSM’s states to specify
properties that should hold; but keep in mind that in black
box testing you cannot just inspect objects state at will.
• Useful concepts : mutators and inspectors.
• Mutators : methods with side effect  arrows in the FSM.
• Inspectors : methods with no side effect  used to express
your state predicates,
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Partitioning the inputs
save(String fname, Object o)
fname : (A) existing file
(B) non-existing file
o : (P) null
(Q) non-null serializable
(R) non-null non-serializable
• Based on “your best understanding” of save’s semantic.
• Terminology: characteristic, block. The domain of a
characteristic is divided into disjoint blocks; the union of
these blocks must cover the entire domain of the
characteristic.
• Assumption : values of the same block are “equivalent”
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So, what input values to choose?
save(String fname, Object o)
fname : (A) existing file
(B) non-existing file
o : (P) null
(Q) non-null serializable
(R) non-null non-serializable
• (C4.23, ALL) All combinations must be tested.
|T| = (i: 0i<k: Bi) ; does not scale up.
• (C4.24, EACH CHOICE) Each block must be tested.
|T| = (max i: 0i<k: Bi) ; usually too weak.
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t-wise coverage
A
B
P
Q
X
Y
T : (A,P,X) ,
(A,Q,Y) , ... more?
• (C4.25, pair-wise coverage). Each pair of blocks (from
different characteristics) must be tested.
• (C4.26, t-wise coverage). Generalization of pair-wise.
• Obviously stronger than EACH CHOICE, and still
scalable.
• Problem: we just blindly combine; no semantical
awareness.
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Adding a bit of semantic
A
B
P
Q
X
Y
Z
Example: t0 = (A,P,X), generates these
additional test requirements :
(B,P,X)
(A,Q,X)
(A,P,Y) (A,P,Z)
• (C4.27, Base Choice Coverage, BCC) Decide a single
base test t0. Make more tests by each time removing
one block from t0, and forming combinations with all
remaining blocks (of the same characteristics).
|T| = 1 + (i : 0i<k : Bi - 1)
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Or, more bits of semantics
A
B
P
Q
X
Y
Z
Example, base tests = (A,P,X), (A,P,Y)
(A,P,X) generates
(B,P,X)
(A,Q,X)
(A,P,Z)
(A,P,Y) generates
(B,P,Y)
(A,Q,Y)
(A,P,Z)
• (C4.28, Multiple Base Choices). For each
characteristic we decide at least one base block.
Then decide a set of base tests; each only include
base blocks. For each base test, generate more tests
by each time removing one base block, and forming
combinations with remaining non-base blocks.
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|T| at most M + (i : 0i<k : M*(Bi - mi))
Example-2, MBCC
A
B
C
P
Q
R
(B,P,X)
(C,P,X)
(A,R,X)
(A,R,Y)
(B,Q,Y)
(C,Q,Y)
X
Y
Z
Bold : base blocks
Chosen base tests = (A,P,X), (A,Q,Y)
These produce these additional test
requirements:
(A,P,Z)
(A,Q,Z)
• base-blocks are not cross-combined
except as in the base tests.
• non-base blocks are not crosscombined with each other.
• (C4.28, Multiple Base Choices). For each characteristic we decide at least
one base block. Then decide a set of base tests; each only include base
blocks. For each base test, generate more tests by each time removing one
base block, and forming combinations with remaining non-base blocks. 35
Constraints, to exclude non-sensical
cases
• Example:
– combo (A,P,Y) is not allowed.
– if P is selected, then X must also be selected.
• Solvable: pair-wise coverage + (A,P,Y) is not allowed.
• Can be unsolvable, e.g. pair-wise coverage + (A,P) is
not allowed.
• General problem: given a coverage criterion C and a
set of constraints, find a test set T satisfying both.
• In general the problem is not trivial to solve.
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Overview of partition-based coverage
ALL
t-Wise
Multiple Base
Choice Coverage
Pair-Wise
Base Choice
Coverage
EACH
CHOICE
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Regression Test
• To test that a new modification in your program does
not break old functionalities. To be efficient, people
typically reuse existing test sets.
• Usually applied for system-testing, where the
problem is considered as more urgent. Challenge:
very time consuming (hours/days!).
• There are also research to apply it continuously at
the unit level, as you edit your program; see it as
extended type-checking. Result was positive!
(Saff & Enrst, An experimental evaluation of continuous testing during
development. ISSTA 2004)
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Some concepts first...
• Test Selection Problem: suppose P has been modified
to P’. Let T be the test set used on P. Choose a subset
T’T to test P’.
• Obviously, exclude obsolete test cases: those that
can’t execute or whose oracles no longer reflect P’
semantic. Let’s assume: we can identify them.
• You want the selection to be safe : T’ includes all
test-cases in T that will execute differently on P’.
• Only attractive if the cost of calculating T’ + executing
T’ is less than simply re-executing the whole T.
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Idea: select those that pass through
modified code
(orginal)
m(x) { if (d) y = x+1 else y=0 }
(modified)
m(x) { if (d) y = x-1 else y=0 }
• If m is the only method in P that changes, the
obvious strategy is to select only test-cases
that pass through m.
• Better: only select test-cases that pass m’s
“modified” branch.
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Corner case
m(x) { if (d) {
y = x+1 ;
if (e) stmt ;
u=0 }
else if (e) stmt
}
m(x) { if (d) y = x+1 ;
if (e) stmt
}
• The first if is modified by removing an else-branch.
Using the previous strategy means that we have to
select all test-cases that pass m. Yet we see that the
paths [d, e, stmt] and [ d, e] present in both old
and new m; so there is actually no need to select
them.
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Looking at it abstractly with CFG
m(x) { if (d) {
y = x+1 ;
if (e) stmt ;
u=0 }
else if (e) stmt
}
m(x) { if (d) y = x+1 ;
if (e) stmt
}
d
y=x+1
e
stmt
d
end
y=x+1
e
stmt
e
u=0
end
stmt
Notice that [d, e, stmt, end] and
[d, e, end] appear in both, and
equivalent.
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Some concepts
• We assume: P is deterministic.  each test-case
always generate the same test path.
• Let p and p’ be the test-paths of a test-case t when
executed on P and P’; t is modification traversing if
not(p  p’).  let’s select modification traversing
test-cases.
• p  p’ if they have the same length, and for each i,
pi  p’i  the latter means they contain the same
sequence of instructions.
• So far this is not helpful, because such a selection
strategy requires us to first execute t on P’. Then it is
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not attractive anymore!
“Intersection” Graph
G:
a
b
G’ :
G’’ = G  G’:
a
b,b
b
c
c
end
d
a,a
c
c,c
end,d
c,c
end,end
end
• First, extend CFG so that branches are labelled by the corresponding
decision value (e.g. T/F for if-branch). Label non-branch edge with some
constant value.
• Each node of G’’ is a pair (u,u’). Then G’’ is defined like this :
– The pair of initial nodes (s0,s0’)  G’’.
– If (u,u’)G’’, and uu’, and uv is an edge in G, and u’v’ and edge in
G’ both with the same label, then (u,u’)  (v,v’) should be an edge in
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G’’.
“Intersection” Graph
G:
a
b
G’ :
G’’ = G  G’:
a
b,b
b
c
c
end
d
a,a
c
c,c
end,d
c,c
end,end
end
• Each path p in G’’ describes how a path in G would be executed on G’ if
the same decisions are taken along the way. Note that this is calculated
without re-executing any test-case on P’.
• Any path in G’’ ends either in a proper exit node (green), or in a pair (u,u’)
where not uv (red). This would be the first time a test-case would hit a
modified code when re-executed on P’.
• The old test-cases are assumed to have been instrumented, so that we
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know which nodes/edges in G it traversed.
Selection Algorithm
G:
a
b
G’ :
G’’ = G  G’:
a
b,b
b
c
c
end
d
a,a
c
c,c
end,d
c,c
end,end
end
• Select test-cases that pass [a,b,c,end] in G  expensive to check!
• (Safe but not minimalistic) Select test-cases that pass a node u in G that is
part of a red-node in G’’.  same problem as before, it will select also
select [a,c,end] which is not modification traversal.
• (Rothermel-Harold, 1997) Select test-cases that pass an edge e in G that in
G’’ leads to a red-node in G’’.  actually the same problem.
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Selection Algorithm
G:
a
b
G’ :
G’’ = G  G’:
a
b
c
c
end
d
b,b
c
end
c,c
end,d
a,a
c,c
end,end
G-partition
NG-partition
• (Ball algorithm,1998) Partition G’’ nodes to those can can reach a greennode (G partition), and those that cannot (NG partition). Look at edges in
G’’ that cross these partitions (so, from G to NG).
A test path p is modification traversing if and only if it passes through a
crossing edge (as meant above).  use this as the selection criterion.
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