diff --git a/src/client/testing/testController/common/utils.ts b/src/client/testing/testController/common/utils.ts
index e3b37bf74e40..9923d7ec3e12 100644
--- a/src/client/testing/testController/common/utils.ts
+++ b/src/client/testing/testController/common/utils.ts
@@ -38,6 +38,22 @@ interface ExecutionResultMessage extends Message {
     params: ExecutionTestPayload;
 }
 
+/**
+ * Retrieves the path to the temporary directory.
+ *
+ * On Windows, it returns the default temporary directory.
+ * On macOS/Linux, it prefers the `XDG_RUNTIME_DIR` environment variable if set,
+ * otherwise, it falls back to the default temporary directory.
+ *
+ * @returns {string} The path to the temporary directory.
+ */
+function getTempDir(): string {
+    if (process.platform === 'win32') {
+        return os.tmpdir(); // Default Windows behavior
+    }
+    return process.env.XDG_RUNTIME_DIR || os.tmpdir(); // Prefer XDG_RUNTIME_DIR on macOS/Linux
+}
+
 /**
  * Writes an array of test IDs to a temporary file.
  *
@@ -50,11 +66,12 @@ export async function writeTestIdsFile(testIds: string[]): Promise<string> {
     const tempName = `test-ids-${randomSuffix}.txt`;
     // create temp file
     let tempFileName: string;
+    const tempDir: string = getTempDir();
     try {
         traceLog('Attempting to use temp directory for test ids file, file name:', tempName);
-        tempFileName = path.join(os.tmpdir(), tempName);
+        tempFileName = path.join(tempDir, tempName);
         // attempt access to written file to check permissions
-        await fs.promises.access(os.tmpdir());
+        await fs.promises.access(tempDir);
     } catch (error) {
         // Handle the error when accessing the temp directory
         traceError('Error accessing temp directory:', error, ' Attempt to use extension root dir instead');
diff --git a/src/test/testing/testController/utils.unit.test.ts b/src/test/testing/testController/utils.unit.test.ts
index ff1a0c707678..4d2af9da3d5a 100644
--- a/src/test/testing/testController/utils.unit.test.ts
+++ b/src/test/testing/testController/utils.unit.test.ts
@@ -2,7 +2,6 @@ import * as assert from 'assert';
 import * as sinon from 'sinon';
 import * as fs from 'fs';
 import * as path from 'path';
-import * as os from 'os';
 import { writeTestIdsFile } from '../../../client/testing/testController/common/utils';
 import { EXTENSION_ROOT_DIR } from '../../../client/constants';
 
@@ -21,11 +20,13 @@ suite('writeTestIdsFile tests', () => {
         const testIds = ['test1', 'test2', 'test3'];
         const writeFileStub = sandbox.stub(fs.promises, 'writeFile').resolves();
 
-        const result = await writeTestIdsFile(testIds);
-
-        const tmpDir = os.tmpdir();
+        // Set up XDG_RUNTIME_DIR
+        process.env = {
+            ...process.env,
+            XDG_RUNTIME_DIR: '/xdg/runtime/dir',
+        };
 
-        assert.ok(result.startsWith(tmpDir));
+        await writeTestIdsFile(testIds);
 
         assert.ok(writeFileStub.calledOnceWith(sinon.match.string, testIds.join('\n')));
     });
@@ -48,3 +49,41 @@ suite('writeTestIdsFile tests', () => {
         assert.ok(writeFileStub.calledOnceWith(sinon.match.string, testIds.join('\n')));
     });
 });
+
+suite('getTempDir tests', () => {
+    let sandbox: sinon.SinonSandbox;
+    let originalPlatform: NodeJS.Platform;
+    let originalEnv: NodeJS.ProcessEnv;
+
+    setup(() => {
+        sandbox = sinon.createSandbox();
+        originalPlatform = process.platform;
+        originalEnv = process.env;
+    });
+
+    teardown(() => {
+        sandbox.restore();
+        Object.defineProperty(process, 'platform', { value: originalPlatform });
+        process.env = originalEnv;
+    });
+
+    test('should use XDG_RUNTIME_DIR on non-Windows if available', async () => {
+        if (process.platform === 'win32') {
+            return;
+        }
+        // Force platform to be Linux
+        Object.defineProperty(process, 'platform', { value: 'linux' });
+
+        // Set up XDG_RUNTIME_DIR
+        process.env = { ...process.env, XDG_RUNTIME_DIR: '/xdg/runtime/dir' };
+
+        const testIds = ['test1', 'test2', 'test3'];
+        sandbox.stub(fs.promises, 'access').resolves();
+        sandbox.stub(fs.promises, 'writeFile').resolves();
+
+        // This will use getTempDir internally
+        const result = await writeTestIdsFile(testIds);
+
+        assert.ok(result.startsWith('/xdg/runtime/dir'));
+    });
+});