Implement whence for SEEK.

lib/Test/MockFile/FileHandle.pm

@@ -402,10 +402,6 @@ Arguments passed are:C<( $self, $pos, $whence )>
 
 Moves the location of our current tell location.
 
-B<$whence is UNIMPLEMENTED>: Open a ticket in
-L<github|https://github.com/cpanelinc/Test-MockFile/issues> if you need
-this feature.
-
 No L<perldoc
 documentation|http://perldoc.perl.org/perltie.html#Tying-FileHandles>
 exists on this method.
@@ -415,17 +411,34 @@ exists on this method.
 sub SEEK {
     my ( $self, $pos, $whence ) = @_;
 
-    if ($whence) {
-        die('Unimplemented');
-    }
     my $file_size = length $self->{'data'}->{'contents'};
     return if $file_size < $pos;
 
-    $self->{'tell'} = $pos;
+    my $new_pos;
+
+    my $SEEK_SET = 0;
+    my $SEEK_CUR = 1;
+    my $SEEK_END = 2;
 
-    return $pos == 0 ? '0 but true' : $pos;
+    if ($whence == $SEEK_SET) {
+        $new_pos = $pos;
+    } elsif ($whence == $SEEK_CUR) {
+        $new_pos = $self->{'tell'} + $pos;
+    } elsif ($whence == $SEEK_END) {
+        $new_pos = $file_size + $pos;
+    } else {
+        die('Invalid whence value');
+    }
+
+    if ($new_pos < 0 || $new_pos > $file_size) {
+        return 0;
+    }
+
+    $self->{'tell'} = $new_pos;
+    return $new_pos == 0 ? '0 but true' : $new_pos;
 }
 
+
 =head2 TELL
 
 Returns the numeric location we are in the file. The C<TELL> tells us

t/sysopen.t

@@ -83,6 +83,21 @@ is( \%Test::MockFile::files_being_mocked, {}, "No mock files are in cache" ) or
     ok( seek( $fh, 0, 0 ), 0, "Seek to start of file returns true" );
     is( sysseek( $fh, 0, 0 ), "0 but true", "sysseek to start of file returns '0 but true' to make it so." );
     ok( sysseek( $fh, 0, 0 ), "sysseek to start of file returns true when checked with ok()" );
+
+    ok( sysseek( $fh, 5,  0 ), "sysseek to position 5 returns true." );
+    ok( sysseek( $fh, 10, 1 ), "Seek 10 bytes forward from the current position." );
+    is( sysseek( $fh, 0,  1 ), 15, "Current position is 15 bytes from start." );
+
+    $buf = "";
+    is( sysread( $fh, $buf, 2, 0 ), 2, "Read 2 bytes from current position (10)." );
+    is( $buf, "PQ", "Line is as expected." );
+
+    ok( sysseek( $fh, -5, 2 ),     "Seek 5 bytes back from end of file." );
+    is( sysseek( $fh, 0,  1 ), 46, "Current position is 46 bytes from start." );
+
+    $buf = "";
+    is( sysread( $fh, $buf, 3, 0 ), 3, "Read 3 bytes from current position (46)." );
+    is( $buf, "vwx", "Line is as expected." );
 }
 
 {
@@ -122,6 +137,23 @@ is( \%Test::MockFile::files_being_mocked, {}, "No mock files are in cache" ) or
     is( sysseek( $fh, 0, 0 ), "0 but true", "sysseek to start of file returns '0 but true' to make it so." );
     ok( sysseek( $fh, 0, 0 ), "sysseek to start of file returns true when checked with ok()" );
 
+    ok( sysseek( $fh, 5,  0 ), "sysseek to position 5 returns true." );
+    ok( sysseek( $fh, 10, 1 ), "Seek 10 bytes forward from the current position." );
+    is( sysseek( $fh, 0,  1 ), 15, "Current position is 15 bytes from start." );
+
+    $buf = "";
+    is( sysread( $fh, $buf, 2, 0 ), 2, "Read 2 bytes from current position (10)." );
+    is( $buf, "PQ", "Line is as expected." );
+
+    ok( sysseek( $fh, -5, 2 ),     "Seek 5 bytes back from end of file." );
+    is( sysseek( $fh, 0,  1 ), 46, "Current position is 46 bytes from start." );
+
+    $buf = "";
+    is( sysread( $fh, $buf, 3, 0 ), 3, "Read 3 bytes from current position (46)." );
+    is( $buf, "vwx", "Line is as expected." );
+
+    like( dies { sysseek( $fh, 10, 3 ) }, qr/Invalid whence value/, "Dies when given an invalid whence value." );
+
     close $fh;
     undef $bar;
 }