Add regression test for detected syntax differing for stdin and files

tests/integration_tests.rs

@@ -1,4 +1,8 @@
 use assert_cmd::Command;
+use std::path::Path;
+use std::str::from_utf8;
+
+const EXAMPLES_DIR: &str = "tests/examples";
 
 fn bat_with_config() -> Command {
     let mut cmd = Command::cargo_bin("bat").unwrap();
@@ -670,3 +674,38 @@ fn do_not_panic_regression_tests() {
             .success();
     }
 }
+
+#[test]
+fn do_not_detect_different_syntax_for_stdin_and_files() {
+    let file = "regression_tests/issue_985.js";
+
+    let output_for_file = bat()
+        .arg("--color=always")
+        .arg("--map-syntax=*.js:Markdown")
+        .arg(&format!("--file-name={}", file))
+        .arg("--style=plain")
+        .arg(file)
+        .assert()
+        .success()
+        .get_output()
+        .stdout
+        .clone();
+
+    let output_for_stdin = bat()
+        .arg("--color=always")
+        .arg("--map-syntax=*.js:Markdown")
+        .arg("--style=plain")
+        .arg(&format!("--file-name={}", file))
+        .pipe_stdin(Path::new(EXAMPLES_DIR).join(file))
+        .unwrap()
+        .assert()
+        .success()
+        .get_output()
+        .stdout
+        .clone();
+
+    assert_eq!(
+        from_utf8(&output_for_file).unwrap(),
+        from_utf8(&output_for_stdin).unwrap()
+    );
+}