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Automated Developer Testing: Achievements and Challenges Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU ASE

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Page 1: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Automated Developer Testing:Achievements and ChallengesTao Xie

North Carolina State University

In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

ASE

Page 2: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Why Automate Testing?

Software testing is important Software errors cost the U.S. economy about $59.5

billion each year (0.6% of the GDP) [NIST 02] Improving testing infrastructure could save 1/3 cost

[NIST 02] Software testing is costly

Account for even half the total cost of software development [Beizer 90]

Automated testing reduces manual testing effort Test execution: JUnit, NUnit, xUnit, etc. Test generation: Pex, AgitarOne, Parasoft Jtest, etc. Test-behavior checking: Pex, AgitarOne, Parasoft Jtest, etc.

Page 3: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Automation in Developer Testing Developer testing

http://www.developertesting.com/ Kent Beck’s 2004 talk on “Future of

Developer Testing”http://www.itconversations.com/shows/detail301.html

This talk focuses on tool automation in developer testing (e.g., unit testing) Not system testing etc. conducted by testers

Page 4: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Software Testing Setup

=?

Outputs

Expected

Outputs

Program

+

Test inputs

Test Oracles

Page 5: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Software Testing Problems

=?

Outputs

Expected

Outputs

Program

+

Test inputs

Test Oracles

Test Generation Generating high-quality test inputs (e.g.,

achieving high code coverage)

Page 6: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Software Testing Problems

=?

Outputs

Expected

Outputs

Program

+

Test inputs

Test Oracles

Test Generation Generating high-quality test inputs (e.g.,

achieving high code coverage)

Test Oracles Specifying high-quality test oracles (e.g.,

guarding against various faults)

Page 7: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

The Recipe of Unit Testing

var list = new List(); list.Add(item); var count = list.Count;

Assert.AreEqual(1, count);}

Three essential ingredients: Data Method Sequence Assertionsvoid Add() { int item = 3;

Page 8: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

The (problem with) Data

Which value matters? Bad choices cause incomplete test

suites. Hard-coded values get stale when

product code changes. Why pick a value if it doesn’t matter?

list.Add(3);

Page 9: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Parameterized Unit Testing

void Add(List list, int item) { var count = list.Count; list.Add(item); Assert.AreEqual(count + 1, list.Count);}

Parameterized Unit Test = Unit Test with Parameters

Separation of concerns Data is generated by a tool Developer can focus on functional

specification

[Tillmann&Schulte ESEC/FSE 05]

Page 10: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Parameterized Unit Tests areAlgebraic Specifications

A Parameterized Unit Test can be read as a universally quantified, conditional axiom.void ReadWrite(string name, string data) { Assume.IsTrue(name != null && data != null); Write(name, data); var readData = Read(name); Assert.AreEqual(data, readData);} string name, string data: name ≠ null data ≠ null ⋀ ⇒ equals( ReadResource(name,WriteResource(name,data)), data)

Page 11: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Parameterized Unit Testingis going mainstreamParameterized Unit Tests (PUTs) commonly

supported by various test frameworks .NET: Supported by .NET test frameworks

http://www.mbunit.com/ http://www.nunit.org/ …

Java: Supported by JUnit 4.X http://www.junit.org/

Generating test inputs for PUTs supported by tools .NET: Supported by Microsoft Research Pex

http://research.microsoft.com/Pex/ Java: Supported by Agitar AgitarOne

http://www.agitar.com/

Page 12: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Test Generation

Human Expensive, incomplete, …

Brute Force Pairwise, predefined data, etc…

Random: Cheap, Fast “It passed a thousand tests” feeling

Dynamic Symbolic Execution: Pex, CUTE,EXE Automated white-box Not random – Constraint Solving

Page 13: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Dynamic Symbolic Execution

Code to generate inputs for:

Constraints to solve

a!=null a!=null &&a.Length>0

a!=null &&a.Length>0 &&a[0]==1234567890

void CoverMe(int[] a){ if (a == null) return; if (a.Length > 0) if (a[0] == 1234567890) throw new Exception("bug");}

Observed constraints

a==nulla!=null &&!(a.Length>0)a!=null &&a.Length>0 &&a[0]!=1234567890

a!=null &&a.Length>0 &&a[0]==1234567890

Data

null

{}

{0}

{123…}a==null

a.Length>0

a[0]==123…T

TF

T

F

F

Execute&MonitorSolve

Choose next path

Done: There is no path left.

Negated condition

Page 14: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Loops Fitnex [Xie et al. DSN 09]

Generic API functions e.g., RegEx matching IsMatch(s1,regex1) Reggae [Li et al. ASE 09-sp]

Method sequences MSeqGen [Thummalapenta et al. ESEC/FSE 09]

Environments e.g., file systems, network, db, … Parameterized Mock Objects [Marri AST 09]

Opportunities Regression testing [Taneja et al. ICSE 09-nier] Developer guidance (cooperative developer testing)

Challenges of DSE

Page 15: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Loops Fitnex [Xie et al. DSN 09]

Generic API functions e.g., RegEx matching IsMatch(s1,regex1) Reggae [Li et al. ASE 09-sp]

Method sequences MSeqGen [Thummalapenta et al. ESEC/FSE 09]

Environments e.g., file systems, network, db, … Parameterized Mock Objects [Marri AST 09]

Applications Test network app at Army division@Fort Hood, Texas Test DB app of hand-held medical assistant device at

FDA

NCSU Industry Tech Transfer

Page 16: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Pex on MSDN DevLabsIncubation Project for Visual Studio

Download counts (20 months)(Feb. 2008 - Oct. 2009 )

Academic: 17,366 Devlabs: 13,022 Total: 30,388

Page 17: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Loops Fitnex [Xie et al. DSN 09]

Generic API functions e.g., RegEx matching IsMatch(s1,regex1) Reggae [Li et al. ASE 09-sp]

Method sequences MSeqGen [Thummalapenta et al. ESEC/FSE 09]

Environments e.g., file systems, network, db, … Parameterized Mock Objects [Marri AST 09]

Applications Test network app at Army division@Fort Hood, Texas Test DB app of hand-held medical assistant device at FDA

NCSU Industry Tech Transfer

Page 18: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

There are decision procedures for individual path conditions, but… Number of potential paths grows

exponentially with number of branches Reachable code not known initially Without guidance, same loop might be

unfolded forever

Fitnex search strategy [Xie et al. DSN 09]

Explosion of Search Space

Page 19: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

public bool TestLoop(int x, int[] y) {if (x == 90) {

for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

Path condition:!(x == 90) ↓New path condition:(x == 90) ↓New test input:TestLoop(90, {0})

Test input:TestLoop(0, {0})

DSE Example

Page 20: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Path condition:(x == 90) && !(y[0] == 15) ↓New path condition:(x == 90) && (y[0] == 15) ↓New test input:TestLoop(90, {15})

Test input:TestLoop(90, {0})

public bool TestLoop(int x, int[] y) {if (x == 90) {

for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

DSE Example

Page 21: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

public bool TestLoop(int x, int[] y) {if (x == 90) {

for (int i = 0; i < y.Length; i++)if (y[i] == 15) x++;

if (x == 110)return true;

} return false;}

Test input:TestLoop(90, {15})

Path condition:(x == 90) && (y[0] == 15) && !(x+1 == 110) ↓New path condition:(x == 90) && (y[0] == 15) && (x+1 == 110) ↓New test input:No solution!?

Challenge in DSE

Page 22: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

public bool TestLoop(int x, int[] y) {if (x == 90) {

for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

Path condition:(x == 90) && (y[0] == 15) && (0 < y.Length) && !(1 < y.Length) && !(x+1 == 110) ↓New path condition:(x == 90) && (y[0] == 15) && (0 < y.Length) && (1 < y.Length)

Expand array size

Test input:TestLoop(90, {15})

A Closer Look

Page 23: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

We can have infinite paths! (both length and number)

Manual analysis need at least 20 loop iterations to cover the target branch

Exploring all paths up to 20 loop iterations is practically infeasible: 220 paths

Test input:TestLoop(90, {15})

public bool TestLoop(int x, int[] y) {if (x == 90) {

for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

A Closer Look

Page 24: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Fitnex: Fitness-Guided Exploration

public bool TestLoop(int x, int[] y) { if (x == 90) { for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

Test input:TestLoop(90, {15, 15})

Our solution: Prefer to flip nodes on the most promising path Prefer to flip the most promising nodes on path Use fitness function as a proxy for promising

Key observations: with respect to the coverage target, not all paths are equally

promising for flipping nodes not all nodes are equally

promising to flip

Page 25: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Fitness Function

FF computes fitness value (distance between the current state and the goal state)

Search tries to minimize fitness value

[Tracey et al. 98, Liu at al. 05, …]

Page 26: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Fitness Function for (x == 110)

public bool TestLoop(int x, int[] y) { if (x == 90) { for (int i = 0; i < y.Length; i++)

if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

Fitness function: |110 – x |

Page 27: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Compute Fitness Values for Paths

(90, {0}) 20(90, {15}) 19(90, {15, 0}) 19(90, {15, 15}) 18(90, {15, 15, 0}) 18(90, {15, 15, 15}) 17(90, {15, 15, 15, 0}) 17(90, {15, 15, 15, 15}) 16(90, {15, 15, 15, 15, 0}) 16(90, {15, 15, 15, 15, 15}) 15…

FitnessValue

(x, y)

Give preference to flip a node in paths with better fitness values.We still need to address which node to flip on paths …

public bool TestLoop(int x, int[] y) {

if (x == 90) { for (int i = 0; i < y.Length; i+

+) if (y[i] == 15) x++;

if (x == 110) return true;

} return false;} Fitness function: |110

– x |

Page 28: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

FitnessValue

Compute Fitness Gains for Branches

public bool TestLoop(int x, int[] y) {

if (x == 90) { for (int i = 0; i < y.Length; i+

+) if (y[i] == 15) x++;

if (x == 110) return true;

} return false;}

(90, {0}) 20(90, {15}) flip b4 19(90, {15, 0}) flip b2 19(90, {15, 15}) flip b4 18(90, {15, 15, 0}) flip b2 18(90, {15, 15, 15}) flip b4 17(90, {15, 15, 15, 0}) flip b2 17(90, {15, 15, 15, 15}) flip b4 16(90, {15, 15, 15, 15, 0}) flip b2 16(90, {15, 15, 15, 15, 15}) flip b4 15…

(x, y)

Fitness function: |110 – x |Branch b1: i < y.LengthBranch b2: i >= y.Length

Branch b3: y[i] == 15Branch b4: y[i] != 15

• Flipping branch node of b4 (b3) gives us average 1 (-1) fitness gain (loss)

• Flipping branch node of b2 (b1) gives us average 0 (0) fitness gain (loss)

Page 29: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Let p be an already explored path, and n a node on that path, with explored outgoing branch b.

After (successfully) flipping n, we get path p’ that goes to node n, and then continues with a different branch b’.

Define fitness gains as follows, where F(.) is the fitness value of a path. Set FGain(b) := F(p) – F(p’) Set FGain(b’) := F(p’) – F(p)

Compute the average fitness gain for each program branch over time

Compute Fitness Gains for Branches

Page 30: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Implementation in Pex

Pex: Automated White-Box Test Generation tool for .NET, based on Dynamic Symbolic Execution

Pex maintains global search frontier All discovered branch nodes are added to frontier Frontier may choose next branch node to flip Fully explored branch nodes are removed from

frontier Pex has a default search frontier

Tries to create diversity across different coverage criteria, e.g. statement coverage, branch coverage, stack traces, etc.

Customizable: Other frontiers can be combined in a fair round-robin scheme

Page 31: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Implementation in Pex

We implemented a new search frontier “Fitnex”:

Nodes to flip are prioritized by their composite fitness value:

F(pn) – FGain(bn),

where pn is path of node n bn is explored outgoing branch of n

Fitnex always picks node with lowest composite fitness value to flip.

To avoid local optimal or biases, the fitness-guided strategy is combined with Pex’s search strategies

Page 32: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

A collection of micro-benchmark programs routinely used by the Pex developers to evaluate Pex’s performance, extracted from real, complex C# programs

Ranging from string matching like

if (value.StartsWith("Hello") && value.EndsWith("World!") && value.Contains(" ")) { … }

to a small parser for a Pascal-like language where the target is to create a legal program.

Evaluation Subjects

Page 33: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Pex with the Fitnex strategy Pex without the Fitnex strategy

Pex’s previous default strategy Random

a strategy where branch nodes to flip are chosen randomly in the already explored execution tree

Iterative Deepening a strategy where breadth-first search is

performed over the execution tree

Search Strategies Under Comparison

Page 34: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

#runs/iterations required to cover the target

Pex w/o Fitnex: avg. improvement of factor 1.9 over RandomPex w/ Fitnex: avg. improvement of factor 5.2 over Random

Evaluation Results

Page 35: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Object Creation

Pex normally uses public methods to configure non-public object fields

Heuristics built-in to deal with common types

User can help if neededvoid (Foo foo) { if (foo.Value == 123) throw …[PexFactoryMethod]Foo Create(Bar bar) { return new Foo(bar);}

Page 36: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

QuickGraph Example

A graph example from QuickGraph library

interface IGraph{ /* Adds given vertex to the graph */ void AddVertex(IVertex v);

/* Creates a new vertex and adds it to the graph */ IVertex AddVertex();

/* Adds an edge to the graph. Both vertices should already exist in the graph */ IEdge AddEdge(IVertex v1, Ivertex v2); }

Page 37: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Method Under Test

Desired object state for reaching targets 1 and 2: graph object should contain vertices and edges

Class SortAlgorithm{ IGraph graph; public SortAlgorithm(IGraph graph) { this.graph = graph; } public void Compute (IVertex s) { foreach(IVertex u in graph.Vertices) { //Target 1 }

foreach(IEdge e in graph.Edges) { //Target 2 } }}

method sequence

Page 38: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Method Under Test

VertexAndEdgeProvider v0 = new VertexAndEdgeProvider();Boolean v1 = false;BidirectionalGraph v2 = new BidirectionalGraph((IVertexAndEdgeProvider)v0, v1);IVertex v3 = v2.AddVertex();IVertex v4 = v0.ProvideVertex();IEdge v15 = v2.AddEdge(v3, v4);

Achieved 31.82% (7 of 22) branch coverageReason for low coverage: Not able to generate graph with vertices and edges

Applying Randoop, a random testing approach that constructs test inputs by randomly selecting method calls

Example sequence generated by Randoop

v4 not in the graph, so edge cannot be added

to graph.

Page 39: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

New MSeqGen Approach

VertexAndEdgeProvider v0;bool bVal;IGraph ag = new AdjacencyGraph(v0, bVal);IVertex source = ag.AddVertex();IVertex target = ag.AddVertex();IVertex vertex3 = ag.AdVertex();IEdge edg1 = ag.AddEdge(source, target);IEdge edg2 = ag.AddEdge(target, vertex3);IEdge edg3 = ag.AddEdge(source, vertex3);

Use mined sequences to assist Randoop and PexBoth Randoop and Pex achieved 86.40% (19 of 22) branch coverage with assistance from MSeqGen

Mine sequences from existing code bases Reuse mined sequences for achieving desired object states

A Mined sequence from an existing codebase

Graph object includes both vertices and edges

Page 40: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Challenges Addressed by MSeqGen

Existing codebases are often large and complete analysis is expensive Search and analyze only relevant portionsConcrete values in mined sequences may be different from desired values Replace concrete values with symbolic values

and use dynamic symbolic executionExtracted sequences individually may not be sufficient to achieve desired object states Combine extracted sequences to generate new

sequences

Page 41: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

MSeqGen: Code Searching

Problem: Existing code bases are often large and complete analysis is expensive Solution:

Use keyword search for identifying relevant method bodies using target classesAnalyze only those relevant method bodies

Target classes: System.Collections.Hashtable QuickGraph.Algorithms.TSAlgorithm

Keywords: Hashtable, TSAlgorithm

Shortnames of target classes are used as

keywords

Page 42: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

MSeqGen: Sequence Generalization

Problem: Concrete values in mined sequences are different from desired values to achieve target statesSolution: Generalize sequences by replacing concrete values with symbolic values

Class A { int f1 { set; get; } int f2 { set; get; } void CoverMe() { if (f1 != 10) return; if (f2 > 25) throw new Exception(“bug”); }}

Method Under Test

A obj = new A();obj.setF1(14);obj.setF2(-10);obj.CoverMe();

Mined Sequence for A

Sequence cannot help in exposing bug since desired values are f1=10 and f2>25

Page 43: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

MSeqGen: Sequence Generalization

Replace concrete values 14 and -10 with symbolic values X1 and X2

A obj = new A();obj.setF1(14);obj.setF2(-10);obj.CoverMe();

Mined Sequence for A int x1 = *, x2 = *;

A obj = new A();obj.setF1(x1);obj.setF2(x2);obj.CoverMe();

Generalized Sequence for A

Use DSE for generating desired values for X1 and X2DSE explores CoverMe method and generates desired values (X1 = 10 and X2 = 35)

Page 44: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Improvement of State-of-the-Art Randoop

Without assistance from MSeqGen: achieved 32% branch coverage achieved 86% branch coverage

In evaluation, help Randoop achieve 8.7% (maximum 20%) higher branch coverage

Pex Without assistance from MSeqGen: achieved 45%

branch coverage achieved 86% branch coverage In evaluation, help Pex achieve 17.4% (maximum 22.5%)

higher branch coverage

Page 45: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Test Oracles

Write assertions and Pex will try to break them

Without assertions, Pex can only find violations of runtime contracts causing NullReferenceException, IndexOutOfRangeException, etc.

Assertions leveraged in product and test code

Pex can leverage Code Contracts

Page 46: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Summary:Automated Developer Testing

=?

Outputs

Expected

Outputs

Program

+

Test inputs

Test Oracles

Test Generation Test inputs for PUT generated by tools (e.g., Pex)

Fitnex: guided exploration of paths [DSN 09] MSeqGen: exploiting real-usage sequences

[ESEC/FSE 09]

Test Oracles Assertions in PUT specified by developers

Division of Labors

Page 47: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Thank you

http://research.microsoft.com/pexhttp://pexase.codeplex.com/ https://sites.google.com/site/asergrp/

Page 48: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Code Contracts

http://research.microsoft.com/en-us/projects/contracts/

Library to state preconditions, postconditions, invariants

Supported by two tools: Static Checker Rewriter: turns Code Contracts into runtime

checks Pex analyses the runtime checks

Contracts act as Test Oracle Pex may find counter examples for

contracts Missing Contracts may be suggested

Page 49: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Example: ArrayList

Class invariant specification:

public class ArrayList { private Object[] _items; private int _size; ...

[ContractInvariantMethod] // attribute comes with Contracts protected void Invariant() { Contract.Invariant(this._items != null); Contract.Invariant(this._size >= 0); Contract.Invariant(this._items.Length >= this._size);

}

Page 50: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

ParameterizedModels

Page 51: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Unit test: while it is debatable what a ‘unit’ is, a ‘unit’ should be small.

Integration test: exercises large portions of a system.

Observation: Integration tests are often “sold” as unit tests

White-box test generation does not scale well to integration test scenarios.

Possible solution: Introduce abstraction layers, and mock components not under test

Unit Testing vs. Integration Testing

Page 52: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

AppendFormat(null, “{0} {1}!”, “Hello”, “World”); “Hello World!”

.Net Implementation:

public StringBuilder AppendFormat( IFormatProvider provider, char[] chars, params object[] args) {

if (chars == null || args == null) throw new ArgumentNullException(…); int pos = 0; int len = chars.Length; char ch = '\x0'; ICustomFormatter cf = null; if (provider != null) cf =

(ICustomFormatter)provider.GetFormat(typeof(ICustomFormatter)); …

ExampleTesting with Interfaces

Page 53: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Introduce a mock class which implements the interface.

Write assertions over expected inputs, provide concrete outputs

public class MFormatProvider : IFormatProvider {

public object GetFormat(Type formatType) { Assert.IsTrue(formatType != null); return new MCustomFormatter(); }}

Problems: Costly to write detailed behavior by example How many and which mock objects do we need to

write?

Stubs / Mock Objects

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Parameterized Mock Objects - 1 Introduce a mock class which implements the

interface. Let an oracle provide the behavior of the mock

methods.

public class MFormatProvider : IFormatProvider {

public object GetFormat(Type formatType) { … object o = call.ChooseResult<object>(); return o; }}

Result: Relevant result values can be generated by white-box test input generation tool, just as other test inputs can be generated! 54

Page 55: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Chosen values can be shaped by assumptions

public class MFormatProvider : IFormatProvider {

public object GetFormat(Type formatType) { … object o = call.ChooseResult<object>(); PexAssume.IsTrue(o is ICustomFormatter);

return o; }}

(Note: Assertions and assumptions are “reversed” when compared to parameterized unit tests.)

Parameterized Mock Objects - 2

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Page 56: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Models from Choices

Choices to build parameterized models

class PFileSystem : IFileSystem { // cached choices PexChosenIndexedValue<string,string> files; string ReadFile(string name) { var content = this.files[name]; if (content == null) throw new FileNotFoundException(); return content; }}

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Subjects: QuickGraph Facebook

Research Questions: RQ1: Can our approach assist Randoop (random

testing tool) in achieving higher code coverages? RQ2: Can our approach assist Pex (DSE-based

testing tool) in achieving higher code coverages?

MSeqGen Evaluation

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RQ1: Assisting Randoop

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RQ2: Assisting Pex

Legend: #c: number of classes P: branch coverage achieved by Pex P + M: branch coverage achieved by Pex and MSeqGen

Page 60: Tao Xie North Carolina State University In collaboration with Nikolai Tillmann, Peli de Halleux, Wolfram Schulte @Microsoft Research and students @NCSU

Assumptions and Assertions

void PexAssume.IsTrue(bool c) { if (!c) throw new AssumptionViolationException();}void PexAssert.IsTrue(bool c) { if (!c) throw new AssertionViolationException();}

Assumptions and assertions induce branches

Executions which cause assumption violations are ignored, not reported as errors or test cases

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How to test this code?(Actual code from .NET base class libraries)

Motivation: Unit Testing HellResourceReader

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Motivation: Unit Testing HellResourceReader

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ResourceReader PUT

[PexClass, TestClass][PexAllowedException(typeof(ArgumentNullException))][PexAllowedException(typeof(ArgumentException))][PexAllowedException(typeof(FormatException))][PexAllowedException(typeof(BadImageFormatException))][PexAllowedException(typeof(IOException))][PexAllowedException(typeof(NotSupportedException))]public partial class ResourceReaderTest { [PexMethod] public unsafe void ReadEntries(byte[] data) { PexAssume.IsTrue(data != null); fixed (byte* p = data) using (var stream = new UnmanagedMemoryStream(p, data.Length)) { var reader = new ResourceReader(stream); foreach (var entry in reader) { /* reading entries */ } } }}

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Creating Complex Objects Exploration of constructor/mutator

method sequences

Testing with class invariants

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Write class invariant as boolean-valued parameterless method Refers to private fields Must be placed in implementation code

Exploration of valid states by setting public/private fields May include states that are not reachable

Object Creation:Class Invariants

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Example: ArrayList

Class invariant specification:

public class ArrayList { private Object[] _items; private int _size; ...

[ContractInvariantMethod] // attribute comes with Contracts protected void Invariant() { Contract.Invariant(this._items != null); Contract.Invariant(this._size >= 0); Contract.Invariant(this._items.Length >= this._size);

}

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Example: ArrayList

PUT:

[PexMethod]public void ArrayListTest(ArrayList al, object o){ int len = al.Count; al.Add(o); PexAssert.IsTrue(al[len] == o);}

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Example: ArrayList

Generated Test:

[TestMethod] public void Add01() { object[] os = new object[0]; // create raw instance ArrayList arrayList = PexInvariant.CreateInstance<ArrayList>();

// set private field via reflection PexInvariant.SetField<object[]>(arrayList, "_items", os); PexInvariant.SetField<int>(arrayList, "_size", 0);

// invoke invariant method via reflection PexInvariant.CheckInvariant(arrayList);

// call to PUT ArrayListTest(arrayList, null); }