Add missing test file.

Author: brammool

src/testdir/test_reltime.vim

@@ -0,0 +1,27 @@
+" Tests for reltime()
+
+if !has('reltime') || !has('float')
+  finish
+endif
+
+func Test_reltime()
+  let now = reltime()
+  sleep 10m
+  let later = reltime()
+  let elapsed = reltime(now)
+  call assert_true(reltimestr(elapsed) =~ '0\.0')
+  call assert_true(reltimestr(elapsed) != '0.0')
+  call assert_true(reltimefloat(elapsed) < 0.1)
+  call assert_true(reltimefloat(elapsed) > 0.0)
+
+  let same = reltime(now, now)
+  call assert_equal('0.000', split(reltimestr(same))[0][:4])
+  call assert_equal(0.0, reltimefloat(same))
+
+  let differs = reltime(now, later)
+  call assert_true(reltimestr(differs) =~ '0\.0')
+  call assert_true(reltimestr(differs) != '0.0')
+  call assert_true(reltimefloat(differs) < 0.1)
+  call assert_true(reltimefloat(differs) > 0.0)
+
+endfunc