(test suite) Added test for dd

Added test "option should be suffixed with ="
This test exhibits the bug (expected failure) that `dd if<TAB>' gets completed
with `\=' instead of `='.

test/lib/completions/dd.exp

@@ -17,4 +17,17 @@ assert_complete_any "dd --"
 sync_after_int
 
 
+set test "option should be suffixed with ="
+set cmd "dd if"
+send "$cmd\t"
+expect -ex "$cmd"
+expect {
+    -re "^=$" { pass $test }
+    -re {^\\=$} { xfail $test }
+}; # expect
+
+
+sync_after_int
+
+
 teardown