tests: clean up/beautify all tests (code style / test style)

testcases/t/51-regress-float-size.t

@@ -3,12 +3,9 @@
 #
 # Regression test for setting a window to floating, tiling and opening a new window
 #
-use Time::HiRes qw(sleep);
 use i3test;
 
-my $tmp = get_unused_workspace;
-cmd "workspace $tmp";
-
+fresh_workspace;
 
 cmd 'open';
 cmd 'mode toggle';