Address comments from @rullzer:

 - implement isAvailable
 - run tests only if ImageMagick with HEIC support is available in the
   environment

Signed-off-by: Sebastian Steinmetz <me@sebastiansteinmetz.ch>

lib/private/Preview/HEIC.php

@@ -29,4 +29,12 @@ class HEIC extends Bitmap {
 	public function getMimeType() {
 		return '/image\/hei(f|c)/';
 	}
+
+	/**
+	 * {@inheritDoc}
+	 */
+	public function isAvailable(\OCP\Files\FileInfo $file) {
+		return in_array("HEIC", \Imagick::queryFonts("HEI*") );
+	}
+
 }

tests/lib/Preview/HEICTest.php

@@ -31,12 +31,18 @@ namespace Test\Preview;
 class HEICTest extends Provider {
 
 	public function setUp() {
-		parent::setUp();
+		if ( !in_array("HEIC", \Imagick::queryFormats("HEI*")) ) {
+			$this->markTestSkipped('ImageMagick is not HEIC aware. Skipping tests');
+		} else {
+			parent::setUp();
+
+			$fileName = 'testimage.heic';
+			$this->imgPath = $this->prepareTestFile($fileName, \OC::$SERVERROOT . '/tests/data/' . $fileName);
+			$this->width = 1680;
+			$this->height = 1050;
+			$this->provider = new \OC\Preview\HEIC;
+		}
 
-		$fileName = 'testimage.heic';
-		$this->imgPath = $this->prepareTestFile($fileName, \OC::$SERVERROOT . '/tests/data/' . $fileName);
-		$this->width = 1680;
-		$this->height = 1050;
-		$this->provider = new \OC\Preview\HEIC;
 	}
+
 }
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