diff --git a/test/bug.360.t b/test/bug.360.t
index 261c36522..a4091a963 100755
--- a/test/bug.360.t
+++ b/test/bug.360.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 6;
+use Test::More tests => 7;
 
 # Create the rc file.
 if (open my $fh, '>', 'bug.rc')
@@ -66,6 +66,9 @@ my ($id) = $output =~ /(\d+)\s+nonrecurring/;
 $output = qx{../src/task rc:bug.rc $id modify due:};
 unlike ($output, qr/You cannot remove the due date from a recurring task./ms, 'Can remove due date from a non-recurring task');
 
+$output = qx{../src/task rc:bug.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key bug.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/bug.932.t b/test/bug.932.t
index fa0bd382b..1d90c126c 100755
--- a/test/bug.932.t
+++ b/test/bug.932.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 11;
+use Test::More tests => 12;
 
 # Create the rc file.
 if (open my $fh, '>', 'bug.rc')
@@ -61,6 +61,9 @@ like ($output, qr/2\s+P.+H.+R/ms, 'Found modified child 0 (propagated from paren
 like ($output, qr/3\s+P.+H.+R/ms, 'Found modified child 1 (propagated from parent)');
 like ($output, qr/4\s+P.+H.+R/ms, 'Found modified child 2 (propagated from parent)');
 
+$output = qx{../src/task rc:bug.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key bug.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/bug.annual.t b/test/bug.annual.t
index 993802e51..887b4234b 100755
--- a/test/bug.annual.t
+++ b/test/bug.annual.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 12;
+use Test::More tests => 13;
 
 # Create the rc file.
 if (open my $fh, '>', 'annual.rc')
@@ -68,6 +68,9 @@ like ($output, qr/9\s+1\/1\/2007\s+(?:-|\d+\ssecs?)\s+foo/,  'synthetic 9 no cre
 like ($output, qr/10\s+1\/1\/2008\s+(?:-|\d+\ssecs?)\s+foo/, 'synthetic 10 no creep');
 like ($output, qr/11\s+1\/1\/2009\s+(?:-|\d+\ssecs?)\s+foo/, 'synthetic 11 no creep');
 
+$output = qx{../src/task rc:annual.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key annual.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/bug.period.t b/test/bug.period.t
index 531c49a14..c0cdb3b39 100755
--- a/test/bug.period.t
+++ b/test/bug.period.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 40;
+use Test::More tests => 41;
 
 # Create the rc file.
 if (open my $fh, '>', 'period.rc')
@@ -153,6 +153,9 @@ like ($output, qr/\b2m\b/,         'verify 2m');
 like ($output, qr/\b2q\b/,         'verify 2q');
 like ($output, qr/\b2y\b/,         'verify 2y');
 
+$output = qx{../src/task rc:period.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key period.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/bug.uuid.t b/test/bug.uuid.t
index 93d8019e7..69d94a606 100755
--- a/test/bug.uuid.t
+++ b/test/bug.uuid.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 4;
+use Test::More tests => 5;
 
 # Create the rc file.
 if (open my $fh, '>', 'uuid.rc')
@@ -81,6 +81,9 @@ $unique_uuids{$uuid} = undef;
 is (scalar (@all_uuids), 6, '6 tasks created');
 is (scalar (keys %unique_uuids), 6, '6 unique UUIDs');
 
+$output = qx{../src/task rc:uuid.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key uuid.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/recur.limit.t b/test/recur.limit.t
index 9139f584d..b0e610916 100755
--- a/test/recur.limit.t
+++ b/test/recur.limit.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 4;
+use Test::More tests => 5;
 
 # Create the rc file.
 if (open my $fh, '>', 'recur.rc')
@@ -50,6 +50,9 @@ $output = qx{../src/task rc:recur.rc rc.recurrence.limit:4 long};
 @tasks = $output =~ /(ONE)/g;
 is (scalar @tasks, 4, 'recurrence.limit override to 4');
 
+$output = qx{../src/task rc:recur.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key recur.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/recur.sort.t b/test/recur.sort.t
index 62a63ffb3..f0baff811 100755
--- a/test/recur.sort.t
+++ b/test/recur.sort.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 4;
+use Test::More tests => 5;
 
 # Create the rc file.
 if (open my $fh, '>', 'recur.rc')
@@ -53,6 +53,9 @@ like ($output, qr/first .* third .* second/msx, 'daily 3d weekly');
 $output = qx{../src/task rc:recur.rc desc};
 like ($output, qr/second .* third .* first/msx, 'weekly 3d daily');
 
+$output = qx{../src/task rc:recur.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key recur.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/recur.t b/test/recur.t
index e923720ab..b1668ccbb 100755
--- a/test/recur.t
+++ b/test/recur.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 10;
+use Test::More tests => 11;
 
 # Create the rc file.
 if (open my $fh, '>', 'recur.rc')
@@ -90,6 +90,9 @@ like ($output, qr/Deleted 1 task\./, '3 deleted');
 # TODO Duplicate a recurring child task
 # TODO Duplicate a recurring parent task
 
+$output = qx{../src/task rc:recur.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key recur.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/recur.until.t b/test/recur.until.t
index 42b419f63..c3861927b 100755
--- a/test/recur.until.t
+++ b/test/recur.until.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 7;
+use Test::More tests => 8;
 
 # Create the rc file.
 if (open my $fh, '>', 'recur.rc')
@@ -55,6 +55,9 @@ qx{../src/task rc:recur.rc 5 do};
 $output = qx{../src/task rc:recur.rc list};
 like ($output, qr/and has been deleted/, 'Parent task deleted');
 
+$output = qx{../src/task rc:recur.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key recur.rc);
 ok (! -r 'pending.data'   &&
diff --git a/test/recur.weekdays.t b/test/recur.weekdays.t
index 615756118..076e715a6 100755
--- a/test/recur.weekdays.t
+++ b/test/recur.weekdays.t
@@ -28,7 +28,7 @@
 
 use strict;
 use warnings;
-use Test::More tests => 4;
+use Test::More tests => 5;
 
 # Create the rc file.
 if (open my $fh, '>', 'recur.rc')
@@ -49,6 +49,9 @@ like ($output, qr/Recurrence\s+weekdays/, 'task recurs every weekday');
 qx{../src/task rc:recur.rc 1 do};
 $output = qx{../src/task rc:recur.rc list};
 
+$output = qx{../src/task rc:recur.rc diag};
+like ($output, qr/No duplicates found/, 'No duplicate UUIDs detected');
+
 # Cleanup.
 unlink qw(pending.data completed.data undo.data backlog.data synch.key recur.rc);
 ok (! -r 'pending.data'   &&