test: improve error emssage reporting in testNapiRun.js

Backport-PR-URL: #19447
PR-URL: #16821
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

test/addons-napi/test_general/testNapiRun.js

@@ -7,6 +7,9 @@ const assert = require('assert');
 // eslint-disable-next-line no-unused-vars
 const addon = require(`./build/${common.buildType}/test_general`);
 
-assert.strictEqual(addon.testNapiRun('(41.92 + 0.08);'), 42,
-                   'napi_run_script() works correctly');
+const testCase = '(41.92 + 0.08);';
+const expected = 42;
+const actual = addon.testNapiRun(testCase);
+
+assert.strictEqual(actual, expected);
 assert.throws(() => addon.testNapiRun({ abc: 'def' }), /string was expected/);