Isolated Parameterized Unit Testing
with Pex and Moles
Nikolai Tillmann, Jonathan “Peli” de Halleux
Microsoft Research
Learning objectives
After I attend this class I will be able to...

Write Unit Tests
 Coverage, assertions, isolation

Use Moles to Isolate Unit Tests
 Test legacy code

Write Pex Parameterized Unit Tests
 Achieve high code coverage
Preparation







We will use Pex for all exercises
Pex includes Moles
Visual Studio 2010 Power Tools
http://research.microsoft.com/Pex
http://www.pexforfun.com
Works with .NET 2, 3.5, 4, x86 and x64
Visual Studio 2008, 2010, Command line
 (Alpha) Silverlight support
Preparation
 Install latest public version
pex.powertool.x86.msi
Unit Testing
Quiz: Unit testing

What is a unit test?
Unit Testing


A unit test is a small program with assertions
Test a single (small) unit of code
void AddAndCount() {
// Arrange
int item = 3;
// Act
var list = new List();
list.Add(item);
// Assert
Assert.AreEqual(1, list.Count);
}
static string ReadFooValue() {
string[] lines =
File.ReadAllLines(@"t:\myapp.ini");
foreach (var line in lines) {
int index = line.IndexOf('=');
string name = line.Substring(0, index);
if (name == "Foo") {
string value = line.Substring(index);
return value;
}
t:\myapp.ini
}
A=B
return null;
}
Foo=C
C=D
Quiz: Code Coverage

How much block coverage do we need?
1. 50%
2. 80%
3. 100%
4. Block coverage alone is not enough
Quiz: Coverage

How much block coverage do we need?
1. 50%
2. 80%
3. 100%
4. Block coverage alone is not enough
▪ Research: no correlation between high code coverage
and quality
Quiz: White box testing
[TestMethod]
void ExistingFoo() {
File.WriteAllLines(@"t:\myapp.ini",new string[]{“Foo=b”});
Reader.ReadFooValue();
}

Do we need more tests to get 100% cov.?
[TestMethod]
void MissingFoo() {
File.WriteAllLines(@"t:\myapp.ini", new string[0]);
Reader.ReadFooValue();
}
Quiz: Assertions

Why write Assertions (or not)?
1. Documentation
2. Double check your program
3. Please your manager
4. Prevent future bugs
5. Validate user inputs
6. Catch errors early
Quiz: Assertions

Why write Assertions (or not)?
1. Documentation
2. Double check your program
3. Please your manager
4. Prevent future bugs
5. Validate user inputs
6. Catch errors early
Quiz: Assertions
[TestMethod]
void MissingFoo() {
File.WriteAllLines(@"t:\myapp.ini",new string[]{“a=b”});
string value = Reader.ReadFooValue();
Assert.IsTrue(????);
}

Which Assertions should you write?
1. Assert.IsTrue(value == “b”);
2. Assert.IsTrue(value == null);
3. Assert.IsTrue(String.IsNullOrEmpty(value))
4. Assert.IsTrue(true);
5. No assertions
Quiz: Assertions
[TestMethod]
void MissingFoo() {
File.WriteAllLines(@"t:\myapp.ini",new string[]{“a=b”});
string value = Reader.ReadFooValue();
Assert.IsTrue(????);
}

Which Assertions should you write?
1. Assert.IsTrue(value == “b”);
2. Assert.IsTrue(value == null);
3. Assert.IsTrue(String.IsNullOrEmpty(value))
4. Assert.IsTrue(true);
5. No assertions
Quiz: Coverage + Assertions

What gives you confidence in the code?
1. High coverage, few assertions
2. Low coverage, many assertions
3. High coverage, many assertions
4. Low coverage, no assertions
5. I wrote it
Quiz: Coverage + Assertions

What gives you confidence in the code?
1. High coverage, few assertions
2. Low coverage, many assertions
3. High coverage, many assertions
▪ Research: Experienced developers write good
assertions, junior developers write ‘debugging’
assertions
4. Low coverage, no assertions
5. I wrote it
string ReadFooValue() {
string[] lines =
File.ReadAllLines(@"t:\myapp.ini");
foreach (var line in lines) {
int index = line.IndexOf('=');
string name = line.Substring(0, index);
if (name == "Foo") {
string value = line.Substring(index + 1);
return value;
}
t:\myapp.ini
}
A=B
return null;
}
Foo=C
C=D
Quiz: Isolation
string ReadFooValue() {
string[] lines = File.ReadAllLines(@"t:\myapp.ini");
...

In the example,
what are the external dependencies?
1. Network Share
2. Local Disk
3. No file system, all in memory
Quiz: Isolation
string ReadFooValue() {
string[] lines = File.ReadAllLines(@"t:\myapp.ini");
...

In the example,
what are the external dependencies?
1. Network Share
2. Local Disk
3. No file system, all in memory
Quiz: Isolation

What is the problem with a Local Disk?
1. Mapping already exists
2. Cannot run tests concurrently
3. Disk full
4. Access rights
Quiz: Isolation

What is the problem with a Local Disk?
1. Mapping already exists
2. Cannot run tests concurrently
3. Disk full
4. Access rights
Unit Testing
Exercise





Map local directory:
> mkdir c:\foo
> net use t: \\[machinename]\c$\foo
Create C# class library, copy in Reader snippet
Create test project, write unit tests
Run unit tests
Optional: Measure code coverage
Definition of Unit Test

What is a good Unit Test?
 A Unit Test is a program
that runs fast the code under test,
without environment dependencies,
with assertions

What is a good Unit Test Suite?
 A set of Unit Tests which achieves
high code coverage
10 Minutes
Break
Isolation with Moles
Dependency hell

Code under test should not depend on hard-coded
environment dependencies:
var lines = File.ReadAllLines(@"t:\myapp.ini");

How do you mitigate the Local Disk issues?
1.
2.
3.
4.
5.
Always run on the same machine, same hardware,
same credentials, same time, same temperature,
same solar system configuration
Refactoring: use Streams
Refactoring: introduce IFileSystem
Refactoring: pass the lines as parameter
Change implementation of File.ReadAllLines
Dependency hell

Code under test should not depend on hard-coded
environment dependencies:
var lines = File.ReadAllLines(@"t:\myapp.ini");

How do you mitigate theReality
Local check
Disk issues?
1.
2.
3.
4.
5.
Always run on the same
machine, same
Refactoring
not hardware,
same credentials, same
time, same
temperature,
always
an option
same solar system configuration
Refactoring: use Streams
Refactoring: introduce IFileSystem
Refactoring: pass the lines as parameter
Change implementation of File.ReadAllLines
Dependency hell

Code under test should not depend on hard-coded
environment dependencies:
var lines = File.ReadAllLines(@"t:\myapp.ini");

How do you mitigate the Local Disk issues?
1.
2.
3.
4.
5.
Always run on the same machine, same hardware,
same credentials, same time, same temperature,
same solar system configuration
Refactoring: use Streams
Refactoring: introduce IFileSystem
Refactoring: pass the lines as parameter
Change implementation of File.ReadAllLines
Dependency hell

Code under test should not depend on hard-coded
environment dependencies:
var lines = File.ReadAllLines(@"t:\myapp.ini");

How do you change File.ReadAllLines?
1. Override static method
2. Changing the CLR (and recompiling it)
3. Rewrite application in JScript
4. Code instrumentation
Dependency hell

Code under test should not depend on hard-coded
environment dependencies:
var lines = File.ReadAllLines(@"t:\myapp.ini");

How do you change File.ReadAllLines?
1. Override static method
2. Changing the CLR (and recompiling it)
3. Rewrite application in JScript
4. Code instrumentation – the Moles framework
Motivation for Moles
 Why another isolation framework?
 Specifically designed to enable Pex
 Simple, Well-defined semantics
▪ “Replace any .NET method”
 Type safe
Moles = Replace any .NET with a delegate
var lines = File.ReadAllLines(@"t:\myapp.ini");
What if we could replace File.ReadAllLines?
File.ReadAllLines
= delegate(string fn)
MFile.ReadAllLinesString = delegate(string fn)
{
return new string[0];
Moles
};
Mole Types Code Generation
// System.IO
public static class File {
public static string[] ReadAllLines(string fn);
}
// System.IO.Moles
public class MFile {
public static
Func<string, string[]> ReadAllLinesString
{ set; }
}
// delegate R Func<T, R>(T t);
Injecting Detours at Runtime
// System.IO
public static class File {
public static string[] ReadAllLines(string fn) {
if (MFile.ReadAllLinesString != null)
return MFile.ReadAllLines(fn);
… original code
}
}
Automatically injected
at runtime
Demo
Quiz: Func<T>

Match the delegates with the methods?
1. Func<string>
a) bool File.Exists(string)
2. Action
b) Console.WriteLine(string)
3. Action<string>
c) void Flush()
4. Func<bool,string>
d) String.Empty {get;}
5. Func<string, bool>
e) List<T>.Capacity {set;}
6. Action<int>
f) string[]
7. Action<List<T>, int>
8. Func<string,string[]>
File.ReadAllLines(string)
Quiz: Func<T>

Match the delegates with the methods?
1. Func<string>
a) bool File.Exists(string)
2. Action
b) Console.WriteLine(string)
3. Action<string>
c) void Flush()
4. Func<bool,string>
d) String.Empty {get;}
5. Func<string, bool>
e) List<T>.Capacity {set;}
6. Action<int>
f) string[]
7. Action<List<T>, int>
8. Func<string,string[]>
File.ReadAllLines(string)
C# 3.0 Lambdas
MFile.ReadAllLinesString =
delegate(string fileName) {
return new string[]{“a=b”};
}
C# 3.0 Lambdas
MFile.ReadAllLinesString =
(fileName) => {
return new string[]{“a=b”};
}
C# 3.0 Lambdas
MFile.ReadAllLinesString =
(fileName) =>
new string[]{“a=b”};
C# 3.0 Lambdas
MFile.ReadAllLinesString =
fileName =>
new string[]{“a=b”};
Quiz: Lambdas

Match the Lambdas with the methods
1. () => “”
a) bool File.Exists(string)
2. () => {}
b) Console.WriteLine(string)
3. s => {}
c) void Flush();
4. (s) => “”
d) String.Empty {get;}
5. (s) => false
e) string ToString();
Quiz: Lambdas

Match the Lambdas with the methods
1. () => “”
a) bool File.Exists(string)
2. () => {}
b) Console.WriteLine(string)
3. s => {}
c) void Flush();
4. (s) => “”
d) String.Empty {get;}
5. (s) => false
e) string ToString();
Moles
Exercise I

Add moles for mscorlib to the test project
 Add new Item
 Moles and Stubs for Testing
 mscorlib.moles



Write test using moles
Run test
Debug test
[TestMethod, ...]
Exercise
II
void ReadFooValueTest()
{
MFile.BehavedAsNotImplemented();
...
static string ReadFooValue() {
if (!File.Exists(@"t:\myapp.ini"))
return null;
string[] lines =
File.ReadAllLines(@"t:\myapp.ini");
...
Exercise II
Constructors and Instance methods
static string ReadFooValue() {
var reader = new StreamReader(“t:\myapp.ini”);
string content = reader.ReadToEnd();
void ReadFooValueTest(string content) {
MStreamReader.ConstructorString =
delegate(StreamReader me, string file) =>
{
var mole = new MStreamReader(me);
mole.ReadToEnd = () => content;
};
static string ReadFooValue() {
var reader
= new StreamReader(@"t:\myapp.ini"))
Exercise
II
var lines = reader.ReadToEnd().Split(‘\n’);
foreach (var line in lines) {
int index = line.IndexOf('=');
string name = line.Substring(0, index);
if (name == "Foo") {
string value = line.Substring(index + 1);
return value;
}
}
return null;
}}
Exercise III
Quiz: Moles Usage

When should you use Moles (and not)?
1.
2.
3.
4.
5.
6.
7.
8.
9.
Always use Moles to solve isolation issues
With Moles, one does not need to use interfaces anymore
Moles only should be used for 3rd party API, use interfaces for
isolation in your APIs
Moles can be used in production code
Moles lets you get away with untestable APIs
Moles make test cases more robust
With Moles, you do not need integration tests anymore
Moles make tests easier to understand
Moles is for poor programmers, real programmers rely on
interfaces
Quiz: Moles Usage

When should you use Moles (and not)?
1.
2.
3.
4.
5.
6.
7.
8.
9.
Always use Moles to solve isolation issues
With Moles, one does not need to use interfaces anymore
Moles only should be used for 3rd party API, use interfaces
for isolation in your APIs
Moles can be used in production code
Moles lets you get away with untestable APIs
Moles make test cases more robust
With Moles, you do not need integration tests anymore
Moles make tests easier to understand
Moles is for poor programmers, real programmers rely on
interfaces
Exercise (optional)
Step-by-Step Tutorials

“Getting Started with Moles”
http://research.microsoft.com/pex/molestutorial.pdf
 “Unit Testing SharePoint Services with Pex”
http://research.microsoft.com/pex/pexsharepoint.pdf

Tip: Check if the external website matches the
version of Pex you installed;
the latest tutorials also ship with the installer.
What you learned so far

The Definition of Unit Testing

Unit Test Isolation through Moles
10 Minutes
Break
Parameterized
Unit Testing
The Recipe of Unit Testing
void AddAndCount() {
int item = 3;
var list = new List();
list.Add(item);
var count = list.Count;
// Arrange
// Act
Assert.AreEqual(1, count); // Assert
}
Quiz: list.Add(???)
list.Add(???);

Which value matters?
1. 0
2. -1, 1
3. int.MaxValue, int.MinValue
4. it does not matter
5. I don’t know until I read the code
Parameterized Unit Testing
void AddAndCount(List list, int item) {
var count = list.Count;
list.Add(item);
Assert.AreEqual(count + 1,
forlist.Count);
any list,
}
for any item,

Separation of
… adding 1 item
 Specification
of behavior
increases Count by 1
 Data to achieve coverage
Problem
Where does the data come from?
 Random data generator
 Real customer data
 Ranges
 Some values hand-picked by dev/tester
 Dynamic Symbolic Execution
Data Generation
by Dynamic Symbolic Execution
Data Generation Challenge
Goal: Given a program with a set of input
parameters, automatically generate a set of input
values that, upon execution, will exercise as many
statements as possible
How would you do it?
60
Dynamic Symbolic Execution
What tests will Pex generate?
Choose next path
Code to generate inputs for:
void CoverMe(int[] a)
{
if (a == null) return;
if (a.Length > 0)
if (a[0] == 1234567890)
throw new Exception("bug");
}
F
F
a.Length>0
a==null
T
Solve
Constraints to solve
Execute&Monitor
Data
Observed constraints
null
a==null
a!=null &&
!(a.Length>0)
a!=null &&
a.Length>0 &&
a[0]!=1234567890
a!=null
{}
a!=null &&
a.Length>0
{0}
a!=null &&
a.Length>0 &&
a[0]==1234567890
{123…}
a!=null &&
a.Length>0 &&
a[0]==1234567890
T
Done: There is no path left.
a[0]==123…
F
T
Dynamic Symbolic Execution
What tests will Pex generate?
What tests will Pex generate?
Choose next path
Solve
void CoverMe2(int[] a, int i)
Constraints to solve
{
if (a[i] == a.Length)
throw new Exception("bug");
}
Execute&Monitor
Data
Observed constraints
Hint: a[i]...
F
F
T
if (a === null)
throw new NullReferenceException();
T
If (i < 0 | i >= a.Length)
throw new ArgumentOutOfRangeException();
F *(a+i)
T
Dynamic Symbolic Execution
What tests will Pex generate?
What tests will Pex generate?
Choose next path
Solve
void CoverMe2(int[] a, int i)
Constraints to solve
{
a[0] = -1;
if (a[i] == a.Length)
throw new Exception("bug");
}
Execute&Monitor
Data
Observed constraints
Hint: a[i]...
F
F
T
if (a === null)
throw new NullReferenceException();
T
if (i < 0 | i >= a.Length)
throw new ArgumentOutOfRangeException();
F *(a+i)
T
Dynamic Symbolic Execution
What tests will Pex generate?
Choose next path
What tests will Pex generate?
void Assert(bool value)
{
if (false == value)
throw new Exception("bug");
}
F
Solve
Constraints to solve
T
T
F
F
T
Execute&Monitor
Data
Observed constraints
Dynamic Symbolic Execution
What tests will Pex generate?
Choose next path
void Foo(int value)
{
Assert(value == 123);
}
void Assert(bool value)
{
if (false == value)
throw new Exception("bug");
}
F
Solve
Constraints to solve
T
T
F
F
T
Execute&Monitor
Data
Observed constraints
Dynamic Symbolic Execution
Demo





Create new project in Visual Studio.
Insert CoverMe method below.
Right-click on CoverMe method,
and select “Run Pex”.
Inspect results in table
public static void CoverMe(int[] a) {
if (a == null) return;
if (a.Length > 0)
if (a[0] == 1234567890)
throw new Exception("bug");
}
How does Pex monitor code?
ldtoken
Point::X
call __Monitor::LDFLD_REFERENCE
ldfld Point::X
call __Monitor::AtDereferenceFallthrough
br
L2
class Point { int x;
static int GetX(Point p) {
if (p != null) return p.X;
else return -1; } }
ldtoken
Point::GetX
call __Monitor::EnterMethod
brfalseL0
ldarg.0
call __Monitor::Argument<Point>
L0: .try {
.try {
call __Monitor::LDARG_0
ldarg.0
call __Monitor::LDNULL
ldnull
call __Monitor::CEQ
ceq
call __Monitor::BRTRUE
brtrue
L1
call __Monitor::BranchFallthrough
call __Monitor::LDARG_0
ldarg.0
…
L1:
call __Monitor::AtBranchTarget
call __Monitor::LDC_I4_M1
ldc.i4.m1
L2:
call __Monitor::RET
stloc.0
leave L4
} catch NullReferenceException {
‘
call __Monitor::AtNullReferenceException
rethrow
}
L4: leave L5
} finally {
call
__Monitor::LeaveMethod
endfinally
}
L5: ldloc.0
ret
(Pex / Moles Architecture)
Pex
Z3
SMT solver
Moles
ExtendedReflection
Dynamic Runtime Analysis
Exercise (Optional / homework)
Code Digging with Pex



Open digger.pdf
http://research.microsoft.com/pex/digger.pdf
Open VS2008
Follow PDF tutorial
 You can pick up initial project from
digger\digger.sln

Stop at section 6: A Glimpse of
Parameterized Unit Tests
Code Digging Exercise
1.
2.
3.
4.
5.
Refactor logic in helper method (as usual)
Make helper method “public”
Right-click “Run Pex” in helper method
Fix bugs
Make helper method “private”
(note: future versions of Pex will support
private methods)
Digger
Exercise
static string ReadFooValue() {
string[] lines = File.ReadAllLines(@"t:\myapp.ini");
return ReadFooValue(lines);
}
public static string ReadFooValue(string[] lines) {
foreach (var line in lines) {
int index = line.IndexOf('=');
string name = line.Substring(0, index);
if (name == "Foo") {
string value = line.Substring(index + 1);
return value;
}
}
return null;
}
10 Minutes
Break
Pex
Parameterized Unit Testing
Test Generation Work-Flow
Code-Under-Test
Project
Test Project
Parameterized
Unit Tests
Pex
Generated Tests
Parameterized Unit Testing
Exercise I – Crash Test



Add a reference to Microsoft.Pex.Framework.dll
Add the following parameterized unit test
“Run Pex Explorations”
using Microsoft.Pex.Framework;
[TestClass, PexClass(typeof(Reader))]
public partial class ReaderTest {
[PexMethod]
public void Crash(string[] lines) {
MFile.ReadAllLines = () => lines;
Reader.ReadFooValue();
}
}
Parameterized Unit Testing
Exercise II – Crash Test




Press “1 Uninstrumented method”
Select row
Click on “Instrument Assembly” (lower right)
Run Pex Explorations again

Execute All Tests in the Solution
Parameterized Unit Testing
Assumptions

Add assumptions and run Pex again
[PexMethod]
public void Crash(string[] lines) {
PexAssume.IsNotNull(lines);
MFile.ReadAllLines = () => lines;
Reader.ReadFooValue();
}
Parameterized Unit Testing
Pex Asserts Observed Results


Manually review outputs
Pex inserts Assertions automatically
[PexMethod]
public string Regression(string[] lines) {
PexAssume.IsNotNull(lines);
MFile.ReadAllLines = () => lines;
// Observe
return Reader.ReadFooValue();
}
Parameterized Unit Testing
Assert something

“Ensure that we parse a Foo entry correctly”
[PexMethod]
void FooExist([PexAssumeNotNull]string value) {
string[] lines = { “Foo=“ + value };
MFile.ReadAllLines = () => lines;
var result = Reader.ReadFooValue();
PexAssert.AreEqual(value, result);
}
Pattern
4A – Assume, Arrange, Act, Assert

Assume, Arrange, Act, Assert
[PexMethod]
void Add(List<T> target, T value) {
// Assume
PexAssume.IsNotNull(target);
// Arrange
var count = target.Count;
// Act
target.Add(value);
// Assert
Assert(target.Count == count + 1);
}
10 Minutes
Break
Pex from the
Command line
pex.exe
pex.exe test.dll
HTML Reports
Rich information, used by Pex developers
Full event log history
Parameter
table
 Code
coverage
 etc…



Limitations
and other Details
It’s called Parameterized Unit Testing
Event Bar

The yellow event bar notifies about
important events, including certain
limitations
Click on issue
kind for more
information
Events View

You should act on these events:
 Refactor your code, or
 tell Pex to ignore it in the future,
 let Pex analyze (“instrument”) more code, if
possible.
Instrumenting more code

If Pex reports that some code was uninstrumented,
you may tell Pex to instrument and analyze it
(if possible)
Instrumenting more code

Code instrumentation on Demand
 Instrumentation has high performance overhead
 Some parts of the code better ignored

Use PexInstrument… attributes
[assembly: PexInstrumentAssembly(“Foo”)]

Pex will often suggest and insert those
attributes for you
Testability

Pex understand managed .NET code only
 Pex does not understand native code.

Problem if branching over values obtained from the
environment
 Pex may not automatically detect all such cases.
File System?
if (!File.Exists(f)) throw ...
Hidden Complexity


Pex analyzes every executed .NET instruction
Some used libraries may be surprisingly expensive
to analyze
 XML parsing
 repeatedly converting data between different
representations
void Sum(string[] A) {
Don’t do this.
var sum = “0”;
foreach(var a in A)
sum = (int.Parse(a) + int.Parse(sum)).ToString();
if(sum == “123”) throw new Exception();
}
Exploration Boundaries

Configurable bounds include:
 TimeOut
 MaxBranches
 MaxCalls
 MaxConditions
▪ Number of conditions that depend on test inputs
 MaxRuns
 ConstraintSolverTimeOut
 ConstraintSolverMemoryLimit
Exercise
Limitations
Goal: Understand limitations.

Apply Pex to
public static void Y2kParser(string s)
{
if (DateTime.Parse(s).Year == 2000)
throw new Exception(“found it”);
}
Patterns
for Parameterized Unit Tests
Pattern
Roundtrip

For an API f(x),
f-1(f(x)) = x
for all x
void ToStringParseRoundtrip(int value) {
string s = value.ToString();
int parsed = int.Parse(s);
Assert.AreEqual(parsed, value);
}
Pattern
Reachability

Indicate which portions of a PUT should be
reachable.
[PexAssertReachEventually]
public void Constructor(object input)
{
new Foo(input);
PexAssert.ReachEventually();
}
Pattern
Same Observable Behavior

Given two methods f(x) and g(x), and a method b(y)
that observes the result or the exception behavior of a
method, assert that f(x) and g(x) have same observable
behavior under b, i.e. b(f(x)) = b(g(x)) for all x.
public void ConcatsBehaveTheSame(
string left, string right)
{
PexAssert.AreBehaviorsEqual(
() => StringFormatter.ConcatV1(left, right),
() => StringFormatter.ConcatV2(left, right));
}
Patterns
How to create objects
Tips and tricks
Creating objects is hard
[PexMethod]
void ReaderTest(Reader reader) {
if (reader.Value == “foo”)
...
}
Pex needs an instance of Reader but…
 Reader is abstract…
 Reader has no public constructors…
 Reader has many constructors…
 …
Pex has heuristics but will call for help
Factory methods
Reader
Hand-written factory method:
public static ReaderFactory {
[PexFactoryMethod(Reader)]
public static Reader Create(string value)
{
return Reader.HiddenCreate(value);
}
}
Pex will explore both factory method and PUT!
Object Creation
Exercise
public class Reader {
string fileName;
private Reader(string fileName) {
this.fileName = fileName;
}
public static Reader Create(string fileName)
{
return new Reader(fileName);
}
string ReadFooValue()
{
var lines = File.ReadAllLines(this.fileName);
}
}
Homework
Patterns

Read patterns paper:
patterns.pdf

http://research.microsoft.com/Pex/patterns.pdf
10 Minutes
Break
Pex and Moles Together
Exercise
public class IniReader {
string section;
public IniReader(string section) { this.section = section; }
public string ParseIni(string key) {
using (var reader = new StreamReader(@"t:\myapp.ini")) {
bool inSection = false;
string line;
while((line = reader.ReadLine()) != null) {
if (line[0] == '[' && line[line.Length - 1] == ']') {
string currentSection = line.Substring(1, line.Length - 2);
inSection = currentSection == section;
}
else {
int index = line.IndexOf('=');
if (index > -1){
string currentKey = line.Substring(0, index);
if (key == currentKey) {
return line.Substring(index);
} } } }
return null;
}}
Wrapping up
What you learned today

The Definition of Unit Testing

Unit Test Isolation through Moles

Parameterized Unit Tests with Pex
Where to go from here

Web: http://research.microsoft.com/pex/
 Links to blogs, more documentation, stubs, moles

General questions:
http://social.msdn.microsoft.com/Forums/en-US/pex/
Thank you
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http://research.microsoft.com/pex