Changing "Add to cart" button text in Magento 2.1.0 ( Overriding js file )

You have to override js file from path

vendor/magento/module-catalog/view/frontend/web/js/catalog-add-to-cart.js  

To

app/design/frontend/YourTheme/Packadge/Magento_Catalog/web/js/catalog-add-to-cart.js

You have to changes text which you want to from this file.

Let me know if you have any query.

you need to override, catalog-add-to-cart.js from path,

vendor/magento/module-catalog/view/frontend/web/js

Text is changing from here after ajax call. you can change text here.

The text changed by Javascript after Ajax call. We can take a look:

vendor/magento/module-catalog/view/frontend/web/js/catalog-add-to-cart.js

For the best practice, should use mixins for "overriding":

We can create a module, and then add these files:

app/code/Vendor/Module/view/frontend/requirejs-config.js

var config = {
    config: {
        mixins: {
            'Magento_Catalog/js/catalog-add-to-cart': {
                'Vendor_Module/js/catalog-add-to-cart-mixin': true
            }
        }
    }
};

app/code/Vendor/Module/view/frontend/web/js/catalog-add-to-cart-mixin.js

define([
        'jquery',
        'mage/translate',
        'jquery/ui'
    ],
    function ($, $t) {
        'use strict';

        return function (target) {
            $.widget('mage.catalogAddToCart', target, {
                options: {
                    addToCartButtonTextWhileAdding: $t('Adding Testing...'),
                    addToCartButtonTextAdded: $t('Added Testing'),
                    addToCartButtonTextDefault: $t('Add to Cart Testing')
                }
            });

            return $.mage.catalogAddToCart;
        };
    });