RE: How do I unit test a Dispose method ?

Here's another way of thinking about this -
Whether a member is IDisposable or not is really an implementation issue (as which members comprise an object is private).
So the general question here is how do we get an object to identify all of its IDisposable private methods and invoke Dispose on them in its Dispose.
There are several ways I can think of doing this, all of which are sort of terrible, but then, we're dealing with a true implementation specific problem.

The underlying technique in all cases is going to be the injection of two more members which are IDisposable mocks.

We can try to .emit code at runtime that will add these mocks to the UUT, but - ugh!
Partial classes could work, but then we'd have to mark the original as partial, so - ugh!
The easiest is to subclass the original class and have the (mock) subclass have two (mock) members whose Dispose() must be called. The implementation would, naturally, have to use reflection to find all members and Dispose() of them properly, but that's what we want to see anyway.

The price to pay is that the class cannot be sealed, but that is really not a problem as only API classes should be sealed anyway and if you class serves both as an API and it actually does anything, shame on you :)

.a.



From: [email protected]<mailto:[email protected]> [mailto:[email protected]] On Behalf Of Roy Osherove
Sent: Thursday, January 23, 2014 4:18 AM
To: testdrivendevelopment
Subject: Re: [TDD] How do I unit test a Dispose method ?


Isn't there already an IDisposable interface? which means you can easily create an IDisposable MOCK object and check if dispose was called on it.
all you would do it then have casted IDisposable in the class level that you would access from the dispose method.

public Connection(SecureString password)
{
IDisposable  _myDisposablePassword;
  _myPassword = password.Copy(); // creates a clone of the password which needs to be disposed
_myDisposablePassword = _myPassword;
}
public void Dispose()
{
  _myDisposablePassword.Dispose(); // releases any resources it holds
}
On Thu, Jan 23, 2014 at 12:06 PM, Gishu Pillai <[email protected]<mailto:[email protected]>> wrote:

public Connection(SecureString password)
{
  _myPassword = password.Copy(); // creates a clone of the password which needs to be disposed
}
public void Dispose()
{
  _myPassword.Dispose(); // releases any resources it holds
}

SecureString is a .Net framework type. I could wrap it in an adapter to ease testing...but doesn't solve the general problem. Wrapping all member disposable type with interfaces is going to be tedious.
It seems this is a better fit for Static code analysis.
Gishu





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