Temporary test files

There are occasionally times during an automated test needs to create a temporary file during the execution of that test. The problem is that often this file is left behind on the system, or even worse stored in some obscure directory on a server. I say worse because those files will be discovered by someone approximately 9.25 months from the time they were created, and that person will spend about 6.5 hours trying to figure out who they belong to before realizing they are no longer needed and can blow them away.

The test designer must decide whether or not to leave test artifacts once created. My general rule of thumb is if the test run is a  system level (or dirty room) test then it is probably ok to leave any artifacts from previous tests lying about on the local machine. But, if the test run is a integration or component level (or primarily clean room) test, then in order to preserve the clean room environment (in other words, I want to eliminate or control the number of unknown environmental variables) then I probably want to remove any test artifacts that are created during the execution of a test.

There are many ways to create a file and delete a file in an automated test. But, one of the easiest ways is to use File class members in C# to create a file that will automatically delete itself when the automated test ends. The FileOptions enumeration in File.Create method provides additional options for FileStream objects including a member that will automatically delete the file when the thread that created it closes.

 FileStream fs = File.Create(path, bufferSize, FileOptions.DeleteOnClose)

Of course if you wanted to design in the option to delete the file at the end of a test based on some Boolean decision you could simply create the file using WriteAllText(), WriteAllLines() or WriteAllBytes() methods.

Another problem with temporary test files is that the test designer frequently hard-codes a clever name such at “test.txt” to name the temporary file in the test case itself. Then of course, the next test fires off and that test also has a hard-coded file name which also happens to be “text.txt” that will either overwrite the first file, or in the worse case append to it. Again, the tester can easily create a random string generator to generate random strings for use as file names, or use another method that is already built into C#.

Another useful method for creating temporary file names is found in the Path class. The Path class member Path.GetRandomFileName() will generate a random file name. This random file name also includes a random extension which may not be desired, so you can use the Path.ChangeExtension method to automatically generate a randomly named file and change the extension to the desired extension.

 string filename = Path.ChangeExtension(GetRandomFileNamePath.GetRandomFileName(), "txt");

Now, we can create a temporary test file at a desired location (say the My Documents folder) on the local machine with a random name and that file will be automatically deleted at the end of the test.

 FileStream fs = File.Create(Path.Combine(
     Path.ChangeExtension(Path.GetRandomFileName(), "txt")),
     bufferSize, FileOptions.DeleteOnClose);