test(frontend): cover MIME precedence in non-PDF type detection (#6438)

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## Checklist

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- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
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Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
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Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
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frontend/editor/src/core/utils/fileUtils.test.ts

@@ -3,6 +3,7 @@ import {
   isPdfFile,
   detectFileExtension,
   formatFileSize,
+  detectNonPdfFileType,
 } from "@app/utils/fileUtils";
 
 describe("fileUtils", () => {
@@ -94,4 +95,18 @@ describe("fileUtils", () => {
       expect(formatFileSize(1024 * 1024 * 1024)).toBe("1 GB");
     });
   });
+
+  describe("detectNonPdfFileType", () => {
+    it("should prioritize MIME type over extension when they conflict", () => {
+      expect(
+        detectNonPdfFileType({
+          name: "financial-summary.pdf",
+          type: "text/csv",
+        }),
+      ).toBe("csv");
+      expect(
+        detectNonPdfFileType({ name: "diagram.png", type: "application/json" }),
+      ).toBe("json");
+    });
+  });
 });