Adds test (currently failing) to show that a UTF-8 file with BOM is not parsed properly when read using FileSourceFile

Author: ldemidov

tests/testsuite/file-ext-with-bom.json

@@ -0,0 +1,4 @@
+{
+    "debug": true,
+    "production": false
+}

tests/testsuite/file.rs

@@ -67,6 +67,18 @@ fn test_file_ext() {
     assert_eq!(c.get("production").ok(), Some(false));
 }
 
+#[test]
+#[cfg(feature = "json")]
+fn test_file_ext_with_utf8_bom() {
+    let c = Config::builder()
+        .add_source(File::with_name("tests/testsuite/file-ext-with-bom.json"))
+        .build()
+        .unwrap();
+
+    assert_eq!(c.get("debug").ok(), Some(true));
+    assert_eq!(c.get("production").ok(), Some(false));
+}
+
 #[test]
 #[cfg(feature = "json")]
 fn test_file_second_ext() {