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Runtime Fault Injection using TestAPI

Runtime Fault Injection using TestAPI

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Fault injection is a technique for improving the coverage of a test by introducing faults to test code paths, in particular error handling code paths that might otherwise rarely be followed” - wikipedia

TestAPI in its current release supports runtime fault injection. The API is pretty easy to use. It comprises of the following steps

Part\Step#

API

Signature of the function where the fault is injected

This is just a string

Fault conditionspecifies when to trigger the fault

(static methods in BuiltInConditions)

TriggerEveryOnNthCall(int n);

TriggerIfCalledBy(string caller);

TriggerIfStackContains(string method);

TriggerOnNthCall(int n);

TriggerOnNthCallBy(int n, string caller);

Fault – determines what needs to be done when the condition is satisfied

(static methods in BuiltInFaults)

ReturnFault();

ReturnValueFault(object returnValue);

ReturnValueRuntimeFault(string returnValueExpression);

ThrowExceptionFault(Exception exceptionValue);

ThrowExceptionRuntimeFault(string exceptionExpression);

Compose the FaultRule

FaultRule(string method);

FaultRule(string method, ICondition condition, IFault fault);

FaultSession – this is a collection of rules to be applied to the application that is being tested

FaultSession(params FaultRule[] rules);

Setup the FaultSession

(method in FaultSession)

public ProcessStartInfo GetProcessStartInfo(string file);

//The file param is the path to the binary under test

Start the test application

Process.Start(ProcessStartInfo);

 

In code, the above looks something like

string method = "TestApplication.DoSomething()";

ICondition condition = BuiltInConditions.TriggerOnNthCall(2);

IFault fault = BuiltInFaults.ThrowExceptionFault(new ArgumentNullException());

FaultRule rule = new FaultRule(method, condition, fault);

 

FaultSession session = new FaultSession(rule);

ProcessStartInfo processInfo = session.GetProcessStartInfo(@".\TestApplication.exe");

Process p = Process.Start(processInfo);

You can look at more usage scenarios in the docs that come along with the download from Codeplex.

While writing this post, I came across this interesting term Bebugging which involves knowingly adding bugs into code and then using # of bugs unidentified as an indicator of real bugs remaining.

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