Bug#39861:

1. mysqltest.cc - added flush to log file after each executed command in a testcase.
2. mtr shows 20 last lines from test case log file if timeout reached.
3. Optimizing the code by Magnus review.
4. It is partially fix bug#40150

client/mysqltest.cc

@@ -7844,8 +7844,9 @@ int main(int argc, char **argv)
     if ( opt_mark_progress )
       mark_progress(command, parser.current_line);
 
-    /* Write result from command to log file */
+    /* Write result from command to log file immediately */
     log_file.write(&ds_res);
+    log_file.flush();
     dynstr_set(&ds_res, 0);
   }
 

mysql-test/lib/mtr_cases.pm

@@ -688,6 +688,7 @@ sub collect_one_test_case {
   my $tinfo= My::Test->new
     (
      name          => "$suitename.$tname",
+     shortname     => $tname,
      path          => "$testdir/$filename",
 
     );

mysql-test/lib/mtr_io.pl

@@ -19,6 +19,7 @@
 # same name.
 
 use strict;
+use Carp;
 
 sub mtr_fromfile ($);
 sub mtr_tofile ($@);
@@ -26,7 +27,7 @@ sub mtr_tonewfile($@);
 sub mtr_appendfile_to_file ($$);
 sub mtr_grab_file($);
 sub mtr_printfile($);
-sub mtr_lastlinefromfile ($);
+sub mtr_lastlinesfromfile ($$);
 
 # Read a whole file, stripping leading and trailing whitespace.
 sub mtr_fromfile ($) {
@@ -94,17 +95,16 @@ sub mtr_printfile($) {
   return;
 }
 
-sub mtr_lastlinefromfile ($) {
-  my $file=  shift;
+sub mtr_lastlinesfromfile ($$) {
+  croak "usage: mtr_lastlinesfromfile(file,numlines)" unless (@_ == 2);
+  my ($file, $num_lines)= @_; 
   my $text;
-
   open(FILE,"<",$file) or mtr_error("can't open file \"$file\": $!");
-  while (my $line= <FILE>)
-  {
-    $text= $line;
-  }
+  my @lines= reverse <FILE>;
   close FILE;
-  return $text;
+  my $size= scalar(@lines);
+  $num_lines= $size unless ($size >= $num_lines);
+  return join("", reverse(splice(@lines, 0, $num_lines)));
 }
 
 1;

mysql-test/mysql-test-run.pl

@@ -3268,8 +3268,14 @@ sub run_testcase ($) {
     # ----------------------------------------------------
     if ( $proc eq $test_timeout_proc )
     {
+      my $log_file_name= $opt_vardir."/log/".$tinfo->{shortname}.".log";
       $tinfo->{comment}=
         "Test case timeout after $opt_testcase_timeout minute(s)\n\n";
+      if  (-e $log_file_name)
+      {
+        $tinfo->{comment}.=
+	   "== $log_file_name == \n" . mtr_lastlinesfromfile($log_file_name, 20)."\n";
+      }
       $tinfo->{'timeout'}= $opt_testcase_timeout; # Mark as timeout
       run_on_all($tinfo, 'analyze-timeout');
       report_failure_and_restart($tinfo);