lib: move checkIsPromise function to private method in Assert class

Author: miguelmarcondesf

lib/assert.js

@@ -343,11 +343,11 @@ class Assert {
       // Return a rejected promise if `promiseFn` throws synchronously.
       resultPromise = promiseFn();
       // Fail in case no promise is returned.
-      if (!checkIsPromise(resultPromise)) {
+      if (!this.#checkIsPromise(resultPromise)) {
         throw new ERR_INVALID_RETURN_VALUE('instance of Promise',
                                            'promiseFn', resultPromise);
       }
-    } else if (checkIsPromise(promiseFn)) {
+    } else if (this.#checkIsPromise(promiseFn)) {
       resultPromise = promiseFn;
     } else {
       throw new ERR_INVALID_ARG_TYPE(
@@ -372,6 +372,16 @@ class Assert {
     return NO_EXCEPTION_SENTINEL;
   }
 
+  #checkIsPromise(obj) {
+    // Accept native ES6 promises and promises that are implemented in a similar
+    // way. Do not accept thenables that use a function as `obj` and that have no
+    // `catch` handler.
+    return isPromise(obj) ||
+      (obj !== null && typeof obj === 'object' &&
+      typeof obj.then === 'function' &&
+      typeof obj.catch === 'function');
+  }
+
   /**
    * Pure assertion tests whether a value is truthy, as determined
    * by !!value.
@@ -1050,16 +1060,6 @@ class Comparison {
   }
 }
 
-function checkIsPromise(obj) {
-  // Accept native ES6 promises and promises that are implemented in a similar
-  // way. Do not accept thenables that use a function as `obj` and that have no
-  // `catch` handler.
-  return isPromise(obj) ||
-    (obj !== null && typeof obj === 'object' &&
-    typeof obj.then === 'function' &&
-    typeof obj.catch === 'function');
-}
-
 function hasMatchingError(actual, expected) {
   if (typeof expected !== 'function') {
     if (isRegExp(expected)) {