Add test case.

tests/proofmode.ref

@@ -706,3 +706,14 @@ The command has indeed failed with message:
 In nested Ltac calls to "iRevert ( (ident) )" and 
 "iForallRevert (ident)", last call failed.
 Tactic failure: iRevert: k is used in hypothesis "Hk".
+"iLöb_no_sbi"
+     : string
+The command has indeed failed with message:
+In nested Ltac calls to "iLöb as (constr)",
+"iLöbRevert (constr) with (tactic3)",
+"iRevertIntros (constr) with (tactic3)", "iRevertIntros_go", 
+"tac" (bound to iRevertIntros "∗" with tac), "tac" (bound to iRevertIntros
+"∗" with tac), "iRevertIntros (constr) with (tactic3)", 
+"iRevertIntros_go", "tac" (bound to iLöbCore as IH), 
+"tac" (bound to iLöbCore as IH) and "iLöbCore as (constr)", last call failed.
+Tactic failure: iLöb: not a step-indexed BI entailment.

tests/proofmode.v

@@ -928,3 +928,12 @@ Check "iRevert_dep_var".
 Lemma iRevert_dep_var (k : nat) (Φ : nat → PROP) : Φ k -∗ Φ (S k).
 Proof. iIntros "Hk". Fail iRevert (k). Abort.
 End error_tests.
+
+Section error_tests_bi.
+Context {PROP : bi}.
+Implicit Types P Q R : PROP.
+
+Check "iLöb_no_sbi".
+Lemma iLöb_no_sbi P : P.
+Proof. Fail iLöb as "IH". Abort.
+End error_tests_bi.