Add integration test.

tests/integration_tests.rs

@@ -748,6 +748,17 @@ fn env_var_bat_pager_value_bat() {
         .stderr(predicate::str::contains("bat as a pager is disallowed"));
 }
 
+#[test]
+fn bat_error_to_stderr() {
+    bat()
+        .env("BAT_PAGER", "bat")
+        .arg("/tmp")
+        .assert()
+        .failure()
+        .stderr(predicate::str::contains("[bat error]"));
+
+}
+
 #[test]
 fn pager_value_bat() {
     bat()
@@ -1194,6 +1205,10 @@ fn can_print_file_starting_with_cache() {
         .stderr("");
 }
 
+#[test]
+fn send_all_bat_error_to_stderr() {
+}
+
 #[test]
 fn does_not_print_unwanted_file_named_cache() {
     bat_with_config().arg("cach").assert().failure();