Update packages/builtin_test/_test.pony

Co-authored-by: Sean T Allen <[email protected]>

packages/builtin_test/_test.pony

@@ -1775,6 +1775,19 @@ class \nodoc\ iso _TestArrayCopyTo is UnitTest
     src1.copy_to(dest1, 0, 0, 10)
     h.assert_array_eq[U8]([0; 1; 2; 3; 4; 5; 6], dest1)
 
+    // Test that copying from an empty source array leaves 
+    // the destination unchanged
+    try
+      // create an initialized array and then remove it's only element
+      // leaving it empty
+      let src2: Array[U8] = [1]
+      src2.pop()?
+      let dest2: Array[U8] = [0; 1; 2; 3; 4; 5; 6]
+      src2.copy_to(dest2, 0, 0, 10)
+    end
+
+    h.assert_array_eq([0; 1; 2; 3; 4; 5; 6], dest2)
+
 class \nodoc\ iso _TestMath128 is UnitTest
   """
   Test 128 bit integer math.