Engineering Abstractions in Model Checking and Testing. Michael Achenbach Klaus Ostermann

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1 Engineering Abstractions in Model Checking and Testing Michael Achenbach Klaus Ostermann 1

2 This Talk What is abstraction engineering? How can we integrate abstractions with current tools? What more is required in the future? 2

3 Abstraction Engineering Abstraction Program Transformation and Manipulation Model Checking Testing 3

4 Abstraction Engineering Abstract Interpretation Abstraction Program Transformation and Manipulation Model Checking Testing 4

5 Abstraction Engineering Predicate Abstraction Abstraction Abstract Interpretation Program Transformation and Manipulation Model Checking Testing 5

6 Abstraction Engineering Predicate Abstraction Abstraction Mock Objects Abstract Interpretation Program Transformation and Manipulation Model Checking Testing 6

7 Abstraction Engineering Predicate Abstraction Abstraction Mock Objects Environment Models Abstract Interpretation Program Transformation and Manipulation Model Checking Testing 7

8 Abstraction Engineering Abstraction Program Transformation and Manipulation Model Checking Testing Abstraction Engineering 8

9 Abstraction Engineering Setting in this work: Language: Java Model Checker: Java PathFinder Abstraction Program Transformation and Manipulation Model Checking Testing Abstraction Engineering 9

10 Our Notion of Abstraction Implementation variant of a class Has bigger or smaller interface Checks also specifications Generates test input Uses non-determinism, pruning Engineering difficulties in integration Exposure of local variables Access to private data Unwanted auxiliary methods 10

11 How to integrate abstractions into a software system? 11

12 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) 12

13 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) Use explorative method: Check all possible exceptions Check if streams are always closed 13

14 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) Reveal possible null pointer exception 14

15 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) Hard to test with concrete file reader Use abstraction! 15

16 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) Avoid invasive modification of local variables and inheritance hierarchy 16

17 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { filereader.close(); catch (IOException e) {log(e) Avoid invasive modification of local variables and inheritance hierarchy More than one concrete FileReader is in use 17

18 Example: Reading Files Test Robustness FileReader filereader = null; filereader = new FileReader(inputFile); BufferedReader in = new BufferedReader(fileReader); while (in.readline()!= null)...; finally { in.close(); catch (IOException e) {log(e) finally { try Advanced { filereader.close(); dynamic catch (IOException e) {log(e) scoping mechanisms required Avoid invasive modification of local variables and inheritance hierarchy More than one concrete FileReader is in use 18

19 Abstraction of File and FileReader class MyFile abstracts File { boolean exists(){ return?; class MyFileReader abstracts FileReader { public MyFileReader (MyFile f) { if(!f.exists()) throw new FileNotFoundException(); public void close() { if(?) throw new IOException(); 19

20 Abstraction of File and FileReader class MyFile abstracts File { boolean exists(){ return?; Non-deterministic choice of the model checker class MyFileReader abstracts FileReader { public MyFileReader (MyFile f) { if(!f.exists()) throw new FileNotFoundException(); public void close() { if(?) throw new IOException(); 20

21 Abstraction of File and FileReader class MyFile abstracts File { boolean exists(){ return?; Non-deterministic choice of the model checker class MyFileReader abstracts FileReader { public MyFileReader (MyFile f) { if(!f.exists()) throw new FileNotFoundException(); public void close() { if(?) throw new IOException(); Bigger interface 21

22 Analysis of Current Tools Setting: Finding bugs in Java programs Program exploration with Java PathFinder (JPF) Tools for modularization: AspectJ Javassist Java Model Interface (JMI) of JPF 22

23 AspectJ Inter-type declarations allow bigger interfaces Type-safe Mandatory super constructor problem: No class exchange Number of inter-type fields grows with each abstraction 23

24 Javassist and JMI Allow implementation alternative of whole class No static safety Only one abstraction at runtime 24

25 Future Work Formalize requirements of abstraction engineering Scoping / multiple class versions Type safety Evaluate dynamic language features: Dynamic class exchange Dynamic abstraction conversion Analyze dynamic languages: Ruby, Python, LUA, etc. 25

26 Conclusions Engineering problem: How to integrate abstractions into a software system? Useful abstraction engineering tasks supported by current tools but Tools lack expressiveness/local scoping Model checking without abstraction engineering has no future in practice! Thank You! 26

Input from Files. Buffered Reader

Input from Files. Buffered Reader Input from Files Buffered Reader Input from files is always text. You can convert it to ints using Integer.parseInt() We use BufferedReaders to minimize the number of reads to the file. The Buffer reads