Test pt-upgrade host-to-host. Implement diff_query_times(). Export $test_diff from PerconaTest instead of doing diag() in no_diff().

t/pt-upgrade/diff_query_times.t

@@ -0,0 +1,85 @@
+#!/usr/bin/perl
+
+BEGIN {
+   die "The PERCONA_TOOLKIT_BRANCH environment variable is not set.\n"
+      unless $ENV{PERCONA_TOOLKIT_BRANCH} && -d $ENV{PERCONA_TOOLKIT_BRANCH};
+   unshift @INC, "$ENV{PERCONA_TOOLKIT_BRANCH}/lib";
+};
+
+use strict;
+use warnings FATAL => 'all';
+use English qw(-no_match_vars);
+use Test::More;
+use Data::Dumper;
+
+use PerconaTest;
+use Sandbox;
+$Data::Dumper::Indent    = 1;
+$Data::Dumper::Sortkeys  = 1;
+$Data::Dumper::Quotekeys = 0;
+
+require "$trunk/bin/pt-upgrade";
+
+sub test_diff_query_times {
+   my (%args) = @_;
+
+   my $diff = pt_upgrade::diff_query_times(
+      query_time1 => $args{t1},
+      query_time2 => $args{t2},
+   );
+   is_deeply(
+      $diff,
+      $args{expect},
+      "$args{t1} vs. $args{t2}"
+   ) or diag(Dumper($diff));
+}
+
+test_diff_query_times(
+   t1     => 0,
+   t2     => 0,
+   expect => undef,
+);
+
+test_diff_query_times(
+   t1     => 1,
+   t2     => 1,
+   expect => undef,
+);
+
+test_diff_query_times(
+   t1     => 23,
+   t2     => 82,
+   expect => undef,
+);
+
+test_diff_query_times(
+   t1     => 23,
+   t2     => 820,
+   expect => [ 23, 820, 35.7 ],
+);
+
+# Just .01 shy of 1 order of mag. diff.
+test_diff_query_times(
+   t1     => 0.09,
+   t2     => 0.89,
+   expect => undef,
+);
+
+# Exactly 1 order of mag. diff.
+test_diff_query_times(
+   t1     => 0.09,
+   t2     => 0.9,
+   expect => [ 0.09, 0.9, '10.0' ],
+);
+
+# An order of mag. decrease, which is ok.
+test_diff_query_times(
+   t1     => 0.9,
+   t2     => 0.09,
+   expect => undef,
+);
+
+# #############################################################################
+# Done.
+# #############################################################################
+done_testing;