add explicit auth failure test

pam/auth_client_test.cc

@@ -59,6 +59,17 @@ TEST_F(AuthClientTest, AuthOK) {
                            << ", server=" << server;
 }
 
+TEST_F(AuthClientTest, AuthFail) {
+  int result;
+
+  result = auth_client_set_certificate(ac, ssl_ca, ssl_cert, ssl_key);
+  EXPECT_EQ(AC_OK, result) << "set_certificate() error: " << auth_client_strerror(result);
+
+  result = auth_client_authenticate(ac, "user", "bad_password", NULL, "127.0.0.1");
+  EXPECT_NE(AC_OK, result) << "authenticate() didn't fail"
+                           << ", server=" << server;
+}
+
 TEST_F(AuthClientTest, SSLFailsWithBadCertificate) {
   int result;