diff --git a/test/parallel/test-whatwg-encoding-textdecoder.js b/test/parallel/test-whatwg-encoding-textdecoder.js
index c4f919289adf2f..5f9499930a07a0 100644
--- a/test/parallel/test-whatwg-encoding-textdecoder.js
+++ b/test/parallel/test-whatwg-encoding-textdecoder.js
@@ -91,18 +91,35 @@ if (common.hasIntl) {
 }
 
 {
-  const fn = TextDecoder.prototype[inspect];
-  assert.doesNotThrow(() => {
-    fn.call(new TextDecoder(), Infinity, {});
-  });
-
-  [{}, [], true, 1, '', new TextEncoder()].forEach((i) => {
-    common.expectsError(() => fn.call(i, Infinity, {}),
-                        {
-                          code: 'ERR_INVALID_THIS',
-                          type: TypeError,
-                          message: 'Value of "this" must be of type TextDecoder'
-                        });
+  const inspectFn = TextDecoder.prototype[inspect];
+  const decodeFn = TextDecoder.prototype.decode;
+  const {
+    encoding: { get: encodingGetter },
+    fatal: { get: fatalGetter },
+    ignoreBOM: { get: ignoreBOMGetter },
+  } = Object.getOwnPropertyDescriptors(TextDecoder.prototype);
+
+  const instance = new TextDecoder();
+
+  const expectedError = {
+    code: 'ERR_INVALID_THIS',
+    type: TypeError,
+    message: 'Value of "this" must be of type TextDecoder'
+  };
+
+  assert.doesNotThrow(() => inspectFn.call(instance, Infinity, {}));
+  assert.doesNotThrow(() => decodeFn.call(instance));
+  assert.doesNotThrow(() => encodingGetter.call(instance));
+  assert.doesNotThrow(() => fatalGetter.call(instance));
+  assert.doesNotThrow(() => ignoreBOMGetter.call(instance));
+
+  const invalidThisArgs = [{}, [], true, 1, '', new TextEncoder()];
+  invalidThisArgs.forEach((i) => {
+    common.expectsError(() => inspectFn.call(i, Infinity, {}), expectedError);
+    common.expectsError(() => decodeFn.call(i), expectedError);
+    common.expectsError(() => encodingGetter.call(i), expectedError);
+    common.expectsError(() => fatalGetter.call(i), expectedError);
+    common.expectsError(() => ignoreBOMGetter.call(i), expectedError);
   });
 }
 
diff --git a/test/parallel/test-whatwg-encoding-textencoder.js b/test/parallel/test-whatwg-encoding-textencoder.js
index fba5445c81941c..4096a02432e900 100644
--- a/test/parallel/test-whatwg-encoding-textencoder.js
+++ b/test/parallel/test-whatwg-encoding-textencoder.js
@@ -35,17 +35,27 @@ assert(TextEncoder);
 }
 
 {
-  const fn = TextEncoder.prototype[inspect];
-  assert.doesNotThrow(() => {
-    fn.call(new TextEncoder(), Infinity, {});
-  });
-
-  [{}, [], true, 1, '', new TextDecoder()].forEach((i) => {
-    common.expectsError(() => fn.call(i, Infinity, {}),
-                        {
-                          code: 'ERR_INVALID_THIS',
-                          type: TypeError,
-                          message: 'Value of "this" must be of type TextEncoder'
-                        });
+  const inspectFn = TextEncoder.prototype[inspect];
+  const encodeFn = TextEncoder.prototype.encode;
+  const encodingGetter =
+    Object.getOwnPropertyDescriptor(TextEncoder.prototype, 'encoding').get;
+
+  const instance = new TextEncoder();
+
+  const expectedError = {
+    code: 'ERR_INVALID_THIS',
+    type: TypeError,
+    message: 'Value of "this" must be of type TextEncoder'
+  };
+
+  assert.doesNotThrow(() => inspectFn.call(instance, Infinity, {}));
+  assert.doesNotThrow(() => encodeFn.call(instance));
+  assert.doesNotThrow(() => encodingGetter.call(instance));
+
+  const invalidThisArgs = [{}, [], true, 1, '', new TextDecoder()];
+  invalidThisArgs.forEach((i) => {
+    common.expectsError(() => inspectFn.call(i, Infinity, {}), expectedError);
+    common.expectsError(() => encodeFn.call(i), expectedError);
+    common.expectsError(() => encodingGetter.call(i), expectedError);
   });
 }