test: add test cases for setUnrefTimeout.

test/parallel/test-timers-setunreftimeout.js

@@ -0,0 +1,71 @@
+// Flags: --expose-internals
+
+'use strict';
+
+const common = require('../common');
+
+const { strictEqual } = require('assert');
+const { setUnrefTimeout } = require('internal/timers');
+
+// ERR_INVALID_CALLBACK
+{
+  // It throws ERR_INVALID_CALLBACK when first argument is not a function.
+  common.expectsError(
+    () => setUnrefTimeout(),
+    {
+      code: 'ERR_INVALID_CALLBACK',
+      type: TypeError,
+      message: 'Callback must be a function'
+    }
+  );
+}
+
+{
+  let called = false;
+  const timer = setUnrefTimeout(common.mustCall(() => {
+    called = true;
+  }), 1);
+
+  const testTimer = setUnrefTimeout(common.mustCall(() => {
+    strictEqual(called, false, 'unref pooled timer returned before check');
+    clearTimeout(testTimer);
+  }), 1);
+
+  strictEqual(timer.refresh(), timer);
+}
+
+// test case for passing the arguments
+{
+  for (let i = 3; i <= 6; i++) {
+    let called = false;
+    let results = [];
+    let inputArgs = [];
+    // set the input argument params
+    for (let j = 0; j <= i - 3 ; j++) {
+      inputArgs.push(j);
+    }
+
+    const timer = setUnrefTimeout(common.mustCall((args1, args2, args3, args4) => {
+      called = true;
+      results.push(args1);
+      results.push(args2);
+      results.push(args3);
+      results.push(args4);
+    }), 1, inputArgs[0], inputArgs[1], inputArgs[2], inputArgs[3]);
+
+    const testTimer = setTimeout(common.mustCall(() => {
+      strictEqual(called, true,
+                  'unref pooled timer should be returned before check');
+      const maxArgsNum = 4;
+      for (let k = 0; k < maxArgsNum; k++) {
+        // checking the arguments passed to setUnrefTimeout
+        let expect = (k + 3 <= i) ? inputArgs[k] : undefined;
+        strictEqual(expect, results[k],
+                    `result ${k} should be ${inputArgs[k]}. actual ${expect}`);
+      }
+      clearTimeout(testTimer);
+    }), 100);
+
+    strictEqual(timer.refresh(), timer);
+  }
+}