Laravel: How can I assertJson an array - laravel

Question

I am creating a feature test for a Seminar. Everything is working great; I am trying to update my feature test to account for the seminar dates.
Each Seminar can have one or many dates, so I am saving these values as a json field:
// migration:
...
$table->json('dates');
...
Here is what my Seminar model looks like:
// Seminar.php
protected $casts = [
'dates' => 'array',
];
When saving the seminar, I am returning a json resource:
if ($seminar->save()) {
return response()->json(new SeminarResource($seminar), 200);
...
Using Postman, my Seminar looks a like this:
...
"capacity": 100,
"dates": [
"2020-10-15",
"2020-10-16"
],
...
So far so good!
In my test, I am testing that a seminar can be created.
$http->assertStatus(201)
->assertJson([
'type' => 'seminars',
'id' => (string)$response->id,
'attributes' => [
'dates' => $response->attributes->dates, // General error: 25 column index out of range
I've tried to convert the array to a string, or json_encode the value in the resource. I don't think that's the correct way since I am already casting the value as an array in the model.
How can I assert that my dates is returning an array?
+"dates": array:2 [
0 => "2020-10-15"
1 => "2020-10-16"
]
Thank you for your suggestions!
EDIT
When I dd($response->attributes->dates); this is what I'm getting (which is correct).
array:2 [
0 => "2020-10-15"
1 => "2020-10-16"
]
What I'm not sure is how to assert an array like that. Since I'm using faker to generate the date, I don't really know (or care) what the date is, just want to assert that it is in fact an array.
I've tried something like:
'dates' => ['*'],
However, that just adds another element to the array.
EDIT 2
If I make the array a string,
'dates' => json_encode($response->attributes->dates),
I'll get an error like this:
--- Expected
+++ Actual
## ##
- 'dates' => '["2020-10-15","2020-10-16"]',
+ 'dates' =>
+ array (
+ 0 => '2020-10-15',
+ 1 => '2020-10-16',
+ ),
In my database, the values are stored like this:
["2020-10-15","2020-10-16"]
My actual test looks like this:
$http->assertStatus(201)
->assertJsonStructure([
'type', 'id', 'attributes' => [
'name', 'venue', 'dates', 'description', 'created_at', 'updated_at',
],
])
->assertJson([
'type' => 'workshops',
'id' => (string)$response->id,
'attributes' => [
'name' => $response->attributes->name,
'venue' => $response->attributes->venue,
'dates' => $response->attributes->dates,
'description' => $response->attributes->description,
'created_at' => (string)$response->attributes->created_at,
'updated_at' => (string)$response->attributes->updated_at,
],
]);
$this->assertDatabaseHas('workshops', [
'id' => $response->id,
'name' => $response->attributes->name,
'venue' => $response->attributes->venue,
'dates' => $response->attributes->dates,
'description' => $response->attributes->description,
]);