Index: openacs-4/packages/acs-datetime/tcl/test/acs-datetime-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-datetime/tcl/test/acs-datetime-procs.tcl,v
diff -u -r1.3.2.3 -r1.3.2.4
--- openacs-4/packages/acs-datetime/tcl/test/acs-datetime-procs.tcl	18 Aug 2020 18:13:38 -0000	1.3.2.3
+++ openacs-4/packages/acs-datetime/tcl/test/acs-datetime-procs.tcl	19 Aug 2020 12:22:04 -0000	1.3.2.4
@@ -144,6 +144,33 @@
         }
     }
 }
+
+aa_register_case -procs {
+        dt_interval_check
+    } -cats {
+        api
+        production_safe
+    } dt_interval_check {
+        Test dt_interval_check proc.
+} {
+    #
+    # Start of the interval is after the end
+    #
+    set start "2020-08-20"
+    set end "2020-08-19"
+    aa_true "Start > End"   "[expr {[dt_interval_check $start $end] < 0}]"
+    #
+    # Start of the interval is before the end
+    #
+    set end "2020-08-21"
+    aa_true "Start < End"   "[expr {[dt_interval_check $start $end] > 0}]"
+    #
+    # Start and end of the interval are equal
+    #
+    set end "2020-08-20"
+    aa_equals "Start = End" "[dt_interval_check $start $end]" "0"
+}
+
 # Local variables:
 #    mode: tcl
 #    tcl-indent-level: 4