Add unit tests for forced encryption check function

tests/unittests/test_forced_encryption.c

@@ -70,7 +70,8 @@ test_cmd_force_encryption_sets_policy_block(void** state)
     char* args[] = { "policy", "block", NULL };
     expect_cons_show("Force encryption policy has been set to \"block\".");
     assert_true(cmd_force_encryption(NULL, CMD_FORCE_ENCRYPTION, args));
-    assert_string_equal(prefs_get_string(PREF_FORCE_ENCRYPTION_MODE), "block");
+    auto_gchar gchar* pref_force_enc_mode = prefs_get_string(PREF_FORCE_ENCRYPTION_MODE);
+    assert_string_equal(pref_force_enc_mode, "block");
 }
 
 // Test: /force-encryption policy resend-to-confirm sets resend mode.
@@ -80,7 +81,8 @@ test_cmd_force_encryption_sets_policy_resend(void** state)
     char* args[] = { "policy", "resend-to-confirm", NULL };
     expect_cons_show("Force encryption policy has been set to \"resend-to-confirm\".");
     assert_true(cmd_force_encryption(NULL, CMD_FORCE_ENCRYPTION, args));
-    assert_string_equal(prefs_get_string(PREF_FORCE_ENCRYPTION_MODE), "resend-to-confirm");
+    auto_gchar gchar* pref_force_enc_mode = prefs_get_string(PREF_FORCE_ENCRYPTION_MODE);
+    assert_string_equal(pref_force_enc_mode, "resend-to-confirm");
 }
 
 // Test: Unencrypted message blocked when policy is block.