Keep TestClient URIs in the form the server sees them

VS Code lowercases the drive letter on Windows, so the URIs TestClient
sends are "file:///c%3A/...", which the server normalizes to
"file:///c:/...". Normalization doesn't change the case of a path, but
TestClient built its URIs from pathToFileURL, which keeps "C:". On
Windows, diagnostics and messages with URIs no longer matched what the
tests expected.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: jdesrosiers

language-server/src/test/TestClient.ts

@@ -66,9 +66,10 @@ export class TestClient {
     this.serverName = serverName;
     this.watchEnabled = false;
     this.openDocuments = new Set();
-    // The "@" is percent-encoded by toClientUri, so URIs from the client never match normalized URIs as-is
+    // The "@" is percent-encoded by toClientUri, so URIs from the client never match normalized URIs as-is.
+    // URIs are kept in the form the server sees them, which includes VS Code's lowercase drive letter on Windows.
     this.workspaceFolder = mkdtemp(join(tmpdir(), "test-workspace@"))
-      .then((path) => normalizeIri(pathToFileURL(path).toString()));
+      .then((path) => normalizeIri(toClientUri(pathToFileURL(path).toString())));
     this.gitignore = this.workspaceFolder.then(async (rootPath) => {
       const gitignorePath = join(rootPath, ".gitignore");
       try {