doc: update comments on test conditions

test/index.js

@@ -52,12 +52,13 @@ const napiVersion = Number(process.versions.napi)
 const nodeMajorVersion = Number(process.versions.node.match(/\d+/)[0])
 
 if (nodeMajorVersion < 10) {
-  // currently experimental only test if node major version
-  // is set to experimental. We can't use napi_experimental here
-  // as that is not supported as a number on earlier
-  // Node.js versions. Once bigint is in a release
-  // this should be guarded on the napi version
-  // in which bigint was added.
+  // Currently experimental only test if NODE_MAJOR_VERSION
+  // is greater than which it exists.
+  // We can't use NAPI_EXPERIMENTAL nor NAPI_VERSION here for
+  // those definition could presents on not supported Node.js
+  // targets.
+  // Once bigint is in a release this should be guarded on
+  // the NAPI_VERSION in which bigint was added.
   testModules.splice(testModules.indexOf('bigint'), 1);
   testModules.splice(testModules.indexOf('typedarray-bigint'), 1);
 }