--- a/RegressionTests__TimeDurationTest.st	Thu May 10 12:44:54 2018 +0200
+++ b/RegressionTests__TimeDurationTest.st	Thu May 10 13:02:58 2018 +0200
@@ -99,6 +99,48 @@
     self assert:(sum asNanoseconds = 1000001000).
     self assert:(sum asPicoseconds = 1000001000000).
 
+    t1 := TimeDuration fromNanoseconds:100.
+    t2 := TimeDuration fromNanoseconds:15.5.
+    sum := t1 + t2.
+
+    self assert:(sum asNanoseconds = 115).
+    self assert:(sum asPicoseconds = 115500).
+
+
+    "
+     self new test_01_Arithmetic
+    "
+!
+
+test_02_Arithmetic
+    |t1 t2 sum|
+
+    t1 := TimeDuration fromSeconds:1.
+    t2 := TimeDuration fromMilliseconds:1.
+    sum := t1 - t2.
+
+    self assert:(sum asMilliseconds == 999).
+    self assert:(sum asMicroseconds = 999000).
+    self assert:(sum asNanoseconds = 999000000).
+    self assert:(sum asPicoseconds = 999000000000).
+
+
+    t1 := TimeDuration fromSeconds:1.
+    t2 := TimeDuration fromMicroseconds:1.
+    sum := t1 - t2.
+
+    self assert:(sum asMilliseconds == 999).
+    self assert:(sum asMicroseconds = 999999).
+    self assert:(sum asNanoseconds = 999999000).
+    self assert:(sum asPicoseconds = 999999000000).
+
+    t1 := TimeDuration fromNanoseconds:100.
+    t2 := TimeDuration fromNanoseconds:15.5.
+    sum := t1 - t2.
+
+    self assert:(sum asNanoseconds = 84).
+    self assert:(sum asPicoseconds = 84500).
+
 
     "
      self new test_01_Arithmetic