PHPUnit: How do I mock this file system?

Question

Consider the following scenario (this is not production code):

 class MyClass {
    public function myMethod() {
        // create a directory
        $path = sys_get_temp_dir() . '/' . md5(rand());
        if(!mkdir($path)) {
            throw new Exception("mkdir() failed.");
        }

        // create a file in that folder
        $myFile = fopen("$path/myFile.txt", "w");
        if(!$myFile) {
            throw new Exception("Cannot open file handle.");
        }
    }
}

Right, so what's the problem? Code coverage reports that this line is not covered:

throw new Exception("Cannot open file handle.");

Which is correct, but since I'm creating the folder above logically it would seem impossible for the fopen() to fail (except maybe in extreme circumstances, like disk at 100 %).

I could ignore the code from code coverage but thats kind of cheating. Is there any way I can mock the file system so that it can recognise myFile.txt and mock the file system unable to create the file?

score 13 · Accepted Answer · edited Oct 01 '15 at 17:09

13

vfsStream is a stream wrapper for a virtual filesystem that is useful in unit tests to mock the real filesystem. You can install it from composer.

More Info at:

https://github.com/mikey179/vfsStream

https://phpunit.de/manual/current/en/test-doubles.html

edited Oct 01 '15 at 17:09

DanielM

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answered Aug 23 '12 at 00:23

raidenace

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I want the mkdir() to pass and the fopen() to fail with a vfs, but how do I set that up without having two separate functions? – Elliot Chance Aug 23 '12 at 01:34
Check `Mocking the Filesystem` specifically starting from examples `10.15` in the `phpunit.de` link above. The advantage of using vfs is that there is no actual dependencies on the original filesystem. – raidenace Aug 23 '12 at 14:47

score 3 · Answer 2 · answered Aug 28 '12 at 20:03

You could also break the function into 2 methods, one to create the path, and the other to use it. Then, individual tests could be done to ensure the path is created. A second set of tests could check and capture the exception when you try to use a bad path.

score 2 · Answer 3 · answered Aug 23 '12 at 00:23

2

Yes!

You should inject the full path somehow, and don't call sys_get_temp_dir() right in that method.

Any non-existant path should trigger a problem. You don't need VFS for that.

BUT you will get a E_NOTICE (or warning perhaps?) before the exception is triggered. So you should probably first check is_writable, and throw the exception if it returns false.

answered Aug 23 '12 at 00:23

Evert

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In this situation the base path is irrelevant, whether I inject it or not. – Elliot Chance Aug 23 '12 at 01:34
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It is relevant. The easiest, consistent way to make this fail is to change the base path. With `sys_get_temp_dir` you can't ever use VSF, as that base path will always be a real path. – Evert Aug 23 '12 at 09:03

PHPUnit: How do I mock this file system?

3 Answers3

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