test(formatDownloadTitle): add basic test

for some reason this will not run well with `tsx -r esm` though
I've used the built-in node TS runner for now, which works:
`node  --experimental-transform-types`

spec-es6/utils/formatDownloadTitle.spec.ts

@@ -0,0 +1,129 @@
+import { formatDownloadTitle } from "../../src/services/utils.ts";
+import { describe, it, execute, expect } from "../mini_test.ts";
+
+const testCases: [fnValue: Parameters<typeof formatDownloadTitle>, expectedValue: ReturnType<typeof formatDownloadTitle>][] = [
+  // empty fileName tests
+  [
+    ["", "text", ""],
+    "untitled.html"
+  ],
+
+  [
+    ["", "canvas", ""],
+    "untitled.json"
+  ],
+
+  [
+    ["", null, ""],
+    "untitled"
+  ],
+
+  // json extension from type tests
+  [
+    ["test_file", "canvas", ""],
+    "test_file.json"
+  ],
+
+  [
+    ["test_file", "relationMap", ""],
+    "test_file.json"
+  ],
+
+  [
+    ["test_file", "search", ""],
+    "test_file.json"
+  ],
+
+  // extension based on mime type
+  [
+    ["test_file", null, "text/csv"],
+    "test_file.csv"
+  ],
+
+  [
+    ["test_file_wo_ext", "image", "image/svg+xml"],
+    "test_file_wo_ext.svg"
+  ],
+
+  [
+    ["test_file_wo_ext", "file", "application/json"],
+    "test_file_wo_ext.json"
+  ],
+
+  [
+    ["test_file_w_fake_ext.ext", "image", "image/svg+xml"],
+    "test_file_w_fake_ext.ext.svg"
+  ],
+
+  [
+    ["test_file_w_correct_ext.svg", "image", "image/svg+xml"],
+    "test_file_w_correct_ext.svg"
+  ],
+
+  [
+    ["test_file_w_correct_ext.svgz", "image", "image/svg+xml"],
+    "test_file_w_correct_ext.svgz"
+  ],
+
+  [
+    ["test_file.zip", "file", "application/zip"],
+    "test_file.zip"
+  ],
+
+  [
+    ["test_file", "file", "application/zip"],
+    "test_file.zip"
+  ],
+
+  // application/octet-stream tests
+  [
+    ["test_file", "file", "application/octet-stream"],
+    "test_file"
+  ],
+
+  [
+    ["test_file.zip", "file", "application/octet-stream"],
+    "test_file.zip"
+  ],
+
+  [
+    ["test_file.unknown", null, "application/octet-stream"],
+    "test_file.unknown"
+  ],
+
+  // sanitized filename tests
+  [
+    ["test/file", null, "application/octet-stream"],
+    "testfile"
+  ],
+
+  [
+    ["test:file.zip", "file", "application/zip"],
+    "testfile.zip"
+  ],
+
+  [
+    [":::", "file", "application/zip"],
+    ".zip"
+  ],
+
+  [
+    [":::a", "file", "application/zip"],
+    "a.zip"
+  ],
+]
+
+
+describe("utils/formatDownloadTitle unit tests", () => {
+
+  testCases.forEach(testCase => {
+    return it(`With args '${JSON.stringify(testCase[0])}' it should return '${testCase[1]}'`, () => {
+      const [value, expected] = testCase;
+      const actual = formatDownloadTitle(...value);
+      expect(actual).toEqual(expected);
+    })
+  })
+
+})
+
+execute()