[M3uFormat] add basic m3u tests

those are a bit silly, but let's be coherent with other tests

tests/Formats/M3uFormatTest.php

@@ -0,0 +1,29 @@
+<?php
+
+/**
+ * M3uFormat
+ */
+
+namespace RssBridge\Tests\Formats;
+
+require_once __DIR__ . '/BaseFormatTest.php';
+
+use PHPUnit\Framework\TestCase;
+
+class M3uFormatTest extends BaseFormatTest
+{
+    private const PATH_EXPECTED = self::PATH_SAMPLES . 'expectedM3uFormat/';
+
+    /**
+     * @dataProvider sampleProvider
+     * @runInSeparateProcess
+     */
+    public function testOutput(string $name, string $path)
+    {
+        $data = $this->formatData('M3u', $this->loadSample($path));
+
+        $expected = file_get_contents(self::PATH_EXPECTED . $name . '.m3u');
+        $this->assertEquals($expected, $data);
+    }
+}
+

tests/Formats/samples/expectedM3uFormat/feed.common.m3u

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+#EXTM3U

tests/Formats/samples/expectedM3uFormat/feed.empty.m3u

@@ -0,0 +1 @@
+#EXTM3U

tests/Formats/samples/expectedM3uFormat/feed.emptyItems.m3u

@@ -0,0 +1 @@
+#EXTM3U

tests/Formats/samples/expectedM3uFormat/feed.microblog.m3u

@@ -0,0 +1 @@
+#EXTM3U