test: add test cases for setUnrefTimeout.

test/parallel/test-timers-setunreftimeout.js

@@ -0,0 +1,48 @@
+// Flags: --expose-internals
+'use strict';
+
+const common = require('../common');
+
+const { strictEqual } = require('assert');
+const { setUnrefTimeout } = require('internal/timers');
+
+{
+  common.expectsError(
+    () => setUnrefTimeout(),
+    {
+      code: 'ERR_INVALID_CALLBACK',
+      type: TypeError,
+      message: 'Callback must be a function. Received undefined'
+    }
+  );
+}
+
+// Test that setUnrefTimeout correctly passes arguments to the callback
+{
+  const maxArgsNum = 4;
+  for (let i = 0; i < maxArgsNum; i++) {
+    const inputArgs = [];
+    // Set the input argument params
+    for (let j = 0; j <= i; j++) {
+      inputArgs.push(j);
+    }
+
+    const timer = setUnrefTimeout(common.mustCall((...args) => {
+      // Check the number of arguments passed to this callback.
+      strictEqual(args.length, i + 1,
+                  `arguments.length should be ${i + 1}.` +
+                  `actual ${args.length}`
+      );
+      for (let k = 0; k < maxArgsNum; k++) {
+        // Checking the arguments passed to setUnrefTimeout
+        const expected = (k <= i) ? inputArgs[k] : undefined;
+        strictEqual(args[k], expected,
+                    `result ${k} should be ${expected}.` +
+                    `actual ${args[k]}`);
+      }
+      clearTimeout(timer);
+    }), 1, ...inputArgs);
+
+    setTimeout(common.mustCall(), 1);
+  }
+}