diff --git a/tests/Unit/Services/ConversionCostEstimatorTest.php b/tests/Unit/Services/ConversionCostEstimatorTest.php
index 24329a2..4315947 100644
--- a/tests/Unit/Services/ConversionCostEstimatorTest.php
+++ b/tests/Unit/Services/ConversionCostEstimatorTest.php
@@ -41,3 +41,12 @@
 
     expect($cost->amount)->toBe(2);
 });
+
+it('estimates png to webp conversion as one credit', function () {
+    $file = FileRecord::factory()->png()->make(['user_id' => 1]);
+    $converter = app(ConverterRegistry::class)->find('png', 'webp');
+
+    $cost = app(ConversionCostEstimator::class)->estimate($file, $converter, []);
+
+    expect($cost->amount)->toBe(1);
+});