diff --git a/src/behaviors/TestableResponseBehavior.php b/src/behaviors/TestableResponseBehavior.php
index 36db9de..cd25ab7 100644
--- a/src/behaviors/TestableResponseBehavior.php
+++ b/src/behaviors/TestableResponseBehavior.php
@@ -132,6 +132,11 @@ function getJsonContent()
         return json_decode($this->response->content, true);
     }
 
+    function json()
+    {
+        return $this->getJsonContent();
+    }
+
     /**
      * If the response returns HTML you can `querySelector()` to inspect the
      * HTML for specific content. The `querySelector()` method takes a
diff --git a/src/test/RequestBuilders.php b/src/test/RequestBuilders.php
index 1c7b7c6..40a2283 100644
--- a/src/test/RequestBuilders.php
+++ b/src/test/RequestBuilders.php
@@ -83,6 +83,26 @@ function post(string $uri, array $body=[]): TestableResponse
             ->send();
     }
 
+    /**
+     * Similar to `->post()`, while adding aJSON `content-type` and `accept` headers.
+     *
+     * ```php
+     * $this->postJson('/comments', [
+     *   'author' => '...',
+     *   'body' => '...',
+     * ])->assertOk();
+     * ```
+     */
+    function postJson(string $uri, array $body=[]): TestableResponse
+    {
+        return $this->http('post', $uri)
+            ->withCsrfToken()
+            ->setBody($body)
+            ->addHeader('Content-Type', 'application/json')
+            ->addHeader('Accept', 'application/json')
+            ->send();
+    }
+
     /**
      * Maes a `POST` request to Craft with the `action` param filled in to the
      * passed value.
diff --git a/tests/RequestBuilderTest.php b/tests/RequestBuilderTest.php
new file mode 100644
index 0000000..1dcdb41
--- /dev/null
+++ b/tests/RequestBuilderTest.php
@@ -0,0 +1,16 @@
+<?php
+
+it('posts to an action', function () {
+    $this->post('/post-data', ['foo' => 'bar'])
+        ->assertHeader('content-type', 'text/html; charset=UTF-8')
+        ->assertSee('"foo":"bar"')
+        ->assertOk();
+});
+
+it('posts json to an action', function () {
+    $response = $this->postJson('/post-data', ['foo' => 'bar'])
+        ->assertHeader('content-type', 'application/json')
+        ->assertOk();
+
+    expect($response->json())->foo->toBe('bar');
+});
diff --git a/tests/templates/post-data.twig b/tests/templates/post-data.twig
new file mode 100644
index 0000000..f253519
--- /dev/null
+++ b/tests/templates/post-data.twig
@@ -0,0 +1,4 @@
+{% if craft.app.request.getAcceptsJson() %}
+    {% header "Content-Type: application/json" %}
+{% endif %}
+{{ craft.app.request.getBodyParams()|json_encode|raw }}