diff --git a/tests/lib/Files/ObjectStore/ObjectStoreTestCase.php b/tests/lib/Files/ObjectStore/ObjectStoreTestCase.php
index 03e7b9545e0..457d9209c99 100644
--- a/tests/lib/Files/ObjectStore/ObjectStoreTestCase.php
+++ b/tests/lib/Files/ObjectStore/ObjectStoreTestCase.php
@@ -61,6 +61,15 @@ abstract class ObjectStoreTestCase extends TestCase {
 		$this->assertEquals('foobar', stream_get_contents($result));
 	}
 
+	protected function assertOnlyExpectedWarnings(array $warnings): void {
+		$onlyFopenWarnings = array_reduce(
+			$warnings,
+			fn (bool $ok, string $warning) => $ok && str_starts_with($warning, 'fopen('),
+			true,
+		);
+		$this->assertTrue($onlyFopenWarnings);
+	}
+
 	public function testDelete(): void {
 		$stream = $this->stringToStream('foobar');
 
@@ -70,25 +79,39 @@ abstract class ObjectStoreTestCase extends TestCase {
 
 		$instance->deleteObject('2');
 
+		$warnings = [];
 		try {
+			set_error_handler(
+				function (int $errno, string $errstr) use (&$warnings): void {
+					$warnings[] = $errstr;
+				},
+			);
 			// to to read to verify that the object no longer exists
 			$instance->readObject('2');
 			$this->fail();
 		} catch (\Exception $e) {
-			// dummy assert to keep phpunit happy
-			$this->assertEquals(1, 1);
+			$this->assertOnlyExpectedWarnings($warnings);
+		} finally {
+			restore_error_handler();
 		}
 	}
 
 	public function testReadNonExisting(): void {
 		$instance = $this->getInstance();
 
+		$warnings = [];
 		try {
+			set_error_handler(
+				function (int $errno, string $errstr) use (&$warnings): void {
+					$warnings[] = $errstr;
+				},
+			);
 			$instance->readObject('non-existing');
 			$this->fail();
 		} catch (\Exception $e) {
-			// dummy assert to keep phpunit happy
-			$this->assertEquals(1, 1);
+			$this->assertOnlyExpectedWarnings($warnings);
+		} finally {
+			restore_error_handler();
 		}
 	}
 
diff --git a/tests/lib/Files/ObjectStore/S3Test.php b/tests/lib/Files/ObjectStore/S3Test.php
index 2915ada0aab..b75536a214e 100644
--- a/tests/lib/Files/ObjectStore/S3Test.php
+++ b/tests/lib/Files/ObjectStore/S3Test.php
@@ -110,6 +110,13 @@ class S3Test extends ObjectStoreTestCase {
 		$emptyStream = fopen('php://memory', 'r');
 		fwrite($emptyStream, '');
 
+		$warnings = [];
+		set_error_handler(
+			function (int $errno, string $errstr) use (&$warnings): void {
+				$warnings[] = $errstr;
+			},
+		);
+
 		$s3->writeObject('emptystream', $emptyStream);
 
 		$this->assertNoUpload('emptystream');
@@ -126,6 +133,8 @@ class S3Test extends ObjectStoreTestCase {
 		self::assertTrue($thrown, 'readObject with range requests are not expected to work on empty objects');
 
 		$s3->deleteObject('emptystream');
+		$this->assertOnlyExpectedWarnings($warnings);
+		restore_error_handler();
 	}
 
 	/** File size to upload in bytes */