Query multiple custom post types in single loop

I’m aware there are several other posts that cover similar ground to what I’m about to ask.

I have three custom post types running, in addition to ‘posts’. I want to run a loop that pulls all posts categorised under a particular category

 <?php
          $args = array(
    'post_type' => 'testimonial',
    'posts_per_page' => 1,
    'tax_query' => array(
        array ( 
                'taxonomy' => 'testimonial_category',
                'field' => 'slug',
                'terms' => 'home'
    )
)
);
$query = new WP_Query( $args );
                $postcount = 0;
            ?>
            <?php if ($query->have_posts()) : ?>
                <?php while ($query->have_posts()) : $query->the_post(); ?>
                    <?php $postcount++; ?>
//loop here
<?php wp_reset_query(); ?>   

This is the code I have at the moment, not sure how I condense this into pulling in multiply post types from one category.

Just change the post_type bit to:

'post_type' => array('testimonial', 'other_post_type', 'another-post-type'),

Assuming that taxonomy is valid across all 3 post types. Otherwise you’ll have to leave that out.

Why? You can pass an array to post_type field.