Add test.

tests/proofmode.v

@@ -109,6 +109,10 @@ Lemma test_very_fast_iIntros P :
   ∀ x y : nat, (⌜ x = y ⌝ → P -∗ P)%I.
 Proof. by iIntros. Qed.
 
+Definition tc_opaque_test : PROP := tc_opaque (∀ x : nat, ⌜ x = x ⌝)%I.
+Lemma test_iIntros_tc_opaque : tc_opaque_test.
+Proof. by iIntros (x). Qed.
+
 (** Prior to 0b84351c this used to loop, now `iAssumption` instantiates `R` with
 `False` and performs false elimination. *)
 Lemma test_iAssumption_evar_ex_false : ∃ R, R ⊢ ∀ P, P.