Feature test, expected ExactJson

How to get the expected form of json.

Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'{"data":{"childrens":{"name":"Dr.","slug":"dr"},"name":"Prof.","slug":"prof"}}'
+'{"data":[{"childrens":[{"name":"Dr.","slug":"dr"}],"name":"Prof.","slug":"prof"}]}

$response->assertStatus(200)
            ->assertExactJson([

                "data" => [
                    "name" => $categories->name,
                    "slug" => $categories->slug,
                    "childrens" => [
                        "name" => $anotherCategory->name,
                        "slug" => $anotherCategory->slug,
                    ]
                ]

            ]);