Fix directives property in Message to be an array by default

Author: jeremeamia

src/Surfaces/Message.php

@@ -18,7 +18,7 @@ class Message extends Surface
     private const DELETE_ORIGINAL = ['delete_original' => 'true'];
 
     /** @var array|string[] A message can have a directive (e.g., response_type) included along with its blocks. */
-    private $directives;
+    private $directives = [];
 
     /**
      * Configures message to send to the entire channel.

tests/Surfaces/MessageTest.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Jeremeamia\Slack\BlockKit\Tests\Surfaces;
+
+use Jeremeamia\Slack\BlockKit\Surfaces\Message;
+use Jeremeamia\Slack\BlockKit\Tests\TestCase;
+
+/**
+ * @covers \Jeremeamia\Slack\BlockKit\Surfaces\Message
+ */
+class MessageTest extends TestCase
+{
+    /**
+     * @param Message $message
+     * @param string $directiveKey
+     * @param string $directiveValue
+     * @dataProvider provideDirectivesUseCases
+     */
+    public function testCanApplyDirectives(Message $message, string $directiveKey, string $directiveValue)
+    {
+        $data = $message->text('foo')->toArray();
+        $this->assertArrayHasKey('blocks', $data);
+        $this->assertArrayHasKey($directiveKey, $data);
+        $this->assertEquals($directiveValue, $data[$directiveKey]);
+    }
+
+    public function provideDirectivesUseCases()
+    {
+        return [
+            [Message::new()->ephemeral(), 'response_type', 'ephemeral'],
+            [Message::new()->inChannel(), 'response_type', 'in_channel'],
+            [Message::new()->replaceOriginal(), 'replace_original', 'true'],
+            [Message::new()->deleteOriginal(), 'delete_original', 'true'],
+        ];
+    }
+
+    public function testDoesNotApplyDirectivesWhenNotSet()
+    {
+        $data = Message::new()->text('foo')->toArray();
+        $this->assertArrayHasKey('blocks', $data);
+        $this->assertArrayNotHasKey('response_type', $data);
+        $this->assertArrayNotHasKey('replace_original', $data);
+        $this->assertArrayNotHasKey('delete_original', $data);
+    }
+}