Add missing test for relative/absolute path cache convergence

The FileInformationCacheMap (added in #13955) normalizes keys so that
relative and absolute paths to the same file share one cache entry.
This adds the test case that was missing from the original test suite.

Author: cderv

tests/unit/project/file-information-cache.test.ts

@@ -9,7 +9,7 @@
 
 import { unitTest } from "../../test.ts";
 import { assert } from "testing/asserts";
-import { join } from "../../../src/deno_ral/path.ts";
+import { join, relative } from "../../../src/deno_ral/path.ts";
 import {
   ensureFileInformationCache,
   FileInformationCacheMap,
@@ -107,3 +107,26 @@ unitTest(
     );
   },
 );
+
+// deno-lint-ignore require-await
+unitTest(
+  "fileInformationCache - relative and absolute paths share same entry",
+  async () => {
+    const project = createMockProjectContext();
+
+    const absolutePath = join(project.dir, "subdir", "page.qmd");
+    const relativePath = relative(Deno.cwd(), absolutePath);
+
+    const entry1 = ensureFileInformationCache(project, relativePath);
+    const entry2 = ensureFileInformationCache(project, absolutePath);
+
+    assert(
+      entry1 === entry2,
+      "Relative and absolute paths to same file should share a cache entry",
+    );
+    assert(
+      project.fileInformationCache.size === 1,
+      "Should have exactly one cache entry",
+    );
+  },
+);