Test::MockFile - Allows tests to validate code that can interact with files without touching the file system.


Version 0.017


Intercepts file system calls for specific files so unit testing can take place without any files being altered on disk.

This is useful for small tests where file interaction is discouraged.

A strict mode is even provided which can throw a die when files are accessed during your tests!

    # Loaded before Test::MockFile so uses the core perl functions without any hooks.
    use Module::I::Dont::Want::To::Alter;

    use Test::MockFile;

    my $mock_file = Test::MockFile->file("/foo/bar", "contents\ngo\nhere");
    open(my $fh, "<", "/foo/bar") or die; # Does not actually open the file on disk.
    say "ok" if -e $fh;
    close $fh;
    say "ok" if (-f "/foo/bar");
    say "/foo/bar is THIS BIG: " . -s "/foo/bar"

    my $missing_mocked_file = Test::MockFile->file("/foo/baz"); # File starts out missing.
    my $opened = open(my $baz_fh, "<", "/foo/baz"); # File reports as missing so fails.
    say "ok" if !-e "/foo/baz";
    open($baz_fh, ">", "/foo/baz") or die; # open for writing
    print <$baz_fh> "replace contents\n";
    open($baz_fh, ">>", "/foo/baz") or die; # open for append.
    print <$baz_fh> "second line";
    close $baz_fh;
    say $baz->contents;
    # Unmock your file.
    undef $missing_mocked_file;
    # The file check will now happen on file system now the file is no longer mocked.
    say "ok" if !-e "/foo/baz";


If the module is loaded in strict mode, any file checks, open, sysopen, opendir, stat, or lstat will throw a die.

For example:

    use Test::MockFile qw/strict/;

    # This will not die.
    Test::MockFile->file("/bar", "...");
    Test::MockFile->symlink("/foo", "/bar");
    -l "/foo" or print "ok\n";
    open(my $fh, ">", "/foo");
    # All of these will die
    open(my $fh, ">", "/unmocked/file"); # Dies
    sysopen(my $fh, "/other/file", O_RDONLY);
    opendir(my $fh, "/dir");
    -e "/file";
    -l "/file"



Args: ($file, $contents, $stats)

This will make cause $file to be mocked in all file checks, opens, etc.

undef contents means that the file should act like it's not there.

See "Mock Stats" for what goes in this hash ref.


Args: ($file_to_mock, $file_on_disk, $stats)

This will make cause $file to be mocked in all file checks, opens, etc.

If file_on_disk isn't present, then this will die.

See "Mock Stats" for what goes in this hash ref.

Args: ($readlink, $file )

This will cause $file to be mocked in all file checks, opens, etc.

$readlink indicates what "fake" file it points to. If the file $readlink points to is not mocked, it will act like a broken link, regardless of what's on disk.

If $readlink is undef, then the symlink is mocked but not present.(lstat $file is empty.)

Stats are not able to be specified on instantiation but can in theory be altered after the object is created. People don't normally mess with the permissions on a symlink.


Args: ($dir, \@contents, $stats)

This will cause $dir to be mocked in all file checks, and opendir interactions.

@contents should be provided in the sort order you expect to see the files from readdir. NOTE: Because "." and ".." will always be the first things readdir returns, These files are automatically inserted at the front of the array.

See "Mock Stats" for what goes in this hash ref.

Mock Stats

When creating mocked files or directories, we default their stats to:

    Test::MockFile->new( $file, $contents, {
            'dev'       => 0,        # stat[0]
            'inode'     => 0,        # stat[1]
            'mode'      => $mode,    # stat[2]
            'nlink'     => 0,        # stat[3]
            'uid'       => 0,        # stat[4]
            'gid'       => 0,        # stat[5]
            'rdev'      => 0,        # stat[6]
            'atime'     => $now,     # stat[8]
            'mtime'     => $now,     # stat[9]
            'ctime'     => $now,     # stat[10]
            'blksize'   => 4096,     # stat[11]
            'fileno'    => undef,    # fileno()

You'll notice that mode, size, and blocks have been left out of this. Mode is set to 666 (for files) or 777 (for directories), xored against the current umask. Size and blocks are calculated based on the size of 'contents' a.k.a. the fake file.

When you want to override one of the defaults, all you need to do is specify that when you declare the file or directory. The rest will continue to default.

    Test::MockFile->file("/root/abc", "...", {inode => 65, uid => 123, mtime => int((2000-1970) * 365.25 * 24 * 60 * 60 }));

    Test::MockFile->dir("/sbin", "...", { mode => 0700 }));


This class method is called by file/symlink/dir. There is no good reason to call this directly.


Optional Arg: $contents

Reports or updates the current contents of the file.

To update, pass an array ref of strings for a dir or a string for a file. Symlinks have no contents.

Makes the virtual file go away. NOTE: This also works for directories.


Optional Args: ($epoch_time)

This function acts like the UNIX utility touch. It sets atime, mtime, ctime to $epoch_time.

If no arguments are passed, $epoch_time is set to time(). If the file does not exist, contents are set to an empty string.


Returns the stat of a mocked file (does not follow symlinks.)

Optional Arg: $readlink

Returns the stat of a mocked file (does not follow symlinks.) You can also use this to change what your symlink is pointing to.

returns true/false, depending on whether this object is a symlink.


returns true/false, depending on whether this object is a directory.


returns true/false, depending on whether this object is a regular file.


returns the size of the file based on its contents.


returns true or false based on if the file exists right now.


Calculates the block count of the file based on its size.


Optional Arg: $perms

Allows you to alter the permissions of a file. This only allows you to change the 07777 bits of the file permissions. The number passed should be the octal 0755 form, not the alphabetic "755" form


Returns the permissions of the file.


Optional Arg: $new_epoch_time

Returns and optionally sets the mtime of the file if passed as an integer.


Optional Arg: $new_epoch_time

Returns and optionally sets the ctime of the file if passed as an integer.


Optional Arg: $new_epoch_time

Returns and optionally sets the atime of the file if passed as an integer.


Args: ( $code_ref )

You can use add_file_access_hook to add a code ref that gets called every time a real file (not mocked) operation happens. We use this for strict mode to die if we detect your program is unexpectedly accessing files. You are welcome to use it for whatever you like.

Whenever the code ref is called, we pass 2 arguments: $code->($access_type, $at_under_ref). Be aware that altering the variables in $at_under_ref will affect the variables passed to open / sysopen, etc.

One use might be:

    Test::MockFile::add_file_access_hook(sub { my $type = shift; print "$type called at: " . Carp::longmess() } );


Calling this subroutine will clear everything that was passed to add_file_access_hook

How this mocking is done:

Test::MockFile uses 2 methods to mock file access:

-X via Overload::FileCheck

It is currently not possible in pure perl to override stat, lstat and -X operators. In conjunction with this module, we've developed Overload::FileCheck.

This enables us to intercept calls to stat, lstat and -X operators (like -e, -f, -d, -s, etc.) and pass them to our control. If the file is currently being mocked, we return the stat (or lstat) information on the file to be used to determine the answer to whatever check was made. This even works for things like -e _. If we do not control the file in question, we return FALLBACK_TO_REAL_OP() which then makes a normal check.

CORE::GLOBAL:: overrides

Since 5.10, it has been possible to override function calls by defining them. like:

    *CORE::GLOBAL::open = sub(*;$@) {...}

Any code which is loaded AFTER this happens will use the alternate open. This means you can place your use Test::MockFile statement after statements you don't want to be mocked and there is no risk that the code will ever be altered by Test::MockFile.

We oveload the following statements and then return tied handles to enable the rest of the IO functions to work properly. Only open / sysopen are needed to address file operations. However opendir file handles were never setup for tie so we have to override all of opendir's related functions.

  • open

  • sysopen

  • opendir

  • readdir

  • telldir

  • seekdir

  • rewinddir

  • closedir


Todd Rinaldo, <toddr at>


Please report any bugs or feature requests to


You can find documentation for this module with the perldoc command.

    perldoc Test::MockFile

You can also look for information at:


Thanks to Nicolas R., <atoomic at> for help with Overload::FileCheck. This module could not have been completed without it.


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All rights reserved.

This is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.