To ensure seamless testing, I am providing a sample image and PDF file to be used during the testing process. Image: sample.png PDF: sample.pdf Testing 1: Repositories Here are the steps to follow for the TinyMCE Image works with repositories: Log in to your account as the admin user. Navigate to the Site Admin > Plugins > Repositories > Manage repositories. Set the "Enable and visible" value to the Upload a file and Wikimedia repository and let the rest disabled. Navigate to the Edit Profile page. In the description editor toolbar, click the image icon Verify that there is an icon and text "You can drag and drop files here to upload or click to select." and the browse repositories button Navigate back to the Site Admin > Plugins > Repositories > Manage repositories. Disable the Upload a file repository Navigate back to the Edit Profile page. In the description editor toolbar, click the image icon Verify that there is an icon and text "Paste an image link in the field below or click the Browse Repositories button." and the browse repositories button  Navigate back to the Site Admin > Plugins > Repositories > Manage repositories. Disable the Wikimedia repository Navigate back to the Edit Profile page. In the description editor toolbar, click the image icon Verify that there is an icon and text "Paste an image link in the field below." and there is no browse repositories button. Testing 2: Click anywhere inside the drag-and-dropzone Here are the steps to follow for uploading an image: Log in to your account as the admin user. Navigate to the Edit Profile section. Click on the "Image" icon in the toolbar located in the description field. Verify that a drag-and-drop zone with the following message appears - "Drag and drop an image to upload or click to select". Open the Web developer tools and navigate to Network. Select "Regular 3G" from the Throttling dropdown. Click anywhere in the drag-and-drop zone. Verify that you are prompted with the native OS file picker. Ensure that you only see files with the image type, such as *.jpg or *.png. Select an image. Verify that you see a preloader icon with uploading progress in percentage. After the progress hits 100%, verify that you see a loading icon. After the loading is done, verify that you will see the image details. Look for a trash icon on the top right of the image preview box and click it. Verify that you are returned to the initial view. Testing 3: Drag and drop from the OS file manager (Continue from Testing 1) Here are the steps to follow for uploading an image: Open your OS file manager, such as Files, Finder or Explorer. Click and drag a non-image file, such as a PDF, to the drag-and-drop zone. If the file is not an image, you will see a warning message stating that the file type cannot be accepted. Return to your OS file manager. Click and drag an image file to the drag-and-drop zone. You will see a preloader icon indicating the uploading progress in percentage. Once the upload reaches 100%, you will see a loading icon. Once the loading is complete, you will see the image details. Click on the trash icon to delete the uploaded file. Verify that you are returned to the initial view. Testing 4: Insert external image URL (Continue from Testing 2) Here are the steps to add an external URL to an image in TinyMCE editor: In the "Or add via URL" input, paste ' https://placehold.co/600x400.png' Wait for the loading icon to disappear Check if the image details appear Verify that there is a single pixel border around the image, using the standard grey and round corners. Click on the Save button Verify that the warning message "An image must have a description unless it is marked as decorative only." appears Tick the "This image is decorative only" checkbox Select the Custom size radio button Verify there is a help icon near the width and height fields. Click the help icon Verify there is a popup window contains text: This image is just a preview. Changes to its size will be visible after you save it. Verify that the Width input shows 600, the Height input shows 400 and the Keep proportion checkbox is checked Change the width to 300 Verify that the height automatically changes to 200 Uncheck the Keep proportion checkbox Change the width to 600 Verify that the height remains at 200 Click the Save button Check if the image appears in the TinyMCE editor with the exact size we set Click on the image and then on the Image icon on the toolbar Make sure the image details appear with the Custom size radio button selected and the same width and height Click on the Save button. Verify the image appears in the editor.