refactor: use assertNotInstanceOf over assertNull on nullable object return and flip actual/expect on constant check

tests/system/Cache/ResponseCacheTest.php

@@ -128,7 +128,7 @@ public function testCachePageIncomingRequest(): void
 
         $cachedResponse = $pageCache->get($request, new Response($this->appConfig));
 
-        $this->assertNull($cachedResponse);
+        $this->assertNotInstanceOf(ResponseInterface::class, $cachedResponse);
     }
 
     public function testCachePageIncomingRequestWithCacheQueryString(): void
@@ -159,14 +159,14 @@ public function testCachePageIncomingRequestWithCacheQueryString(): void
         $request        = $this->createIncomingRequest('foo/bar', ['xfoo' => 'bar', 'bar' => 'baz']);
         $cachedResponse = $pageCache->get($request, new Response($this->appConfig));
 
-        $this->assertNull($cachedResponse);
+        $this->assertNotInstanceOf(ResponseInterface::class, $cachedResponse);
 
         // Check cache with another request with the different URI path.
         $request = $this->createIncomingRequest('another');
 
         $cachedResponse = $pageCache->get($request, new Response($this->appConfig));
 
-        $this->assertNull($cachedResponse);
+        $this->assertNotInstanceOf(ResponseInterface::class, $cachedResponse);
     }
 
     public function testCachePageIncomingRequestWithHttpMethods(): void
@@ -186,7 +186,7 @@ public function testCachePageIncomingRequestWithHttpMethods(): void
         $request        = $this->createIncomingRequest('foo/bar')->withMethod('POST');
         $cachedResponse = $pageCache->get($request, new Response($this->appConfig));
 
-        $this->assertNull($cachedResponse);
+        $this->assertNotInstanceOf(ResponseInterface::class, $cachedResponse);
     }
 
     public function testCachePageCLIRequest(): void
@@ -214,7 +214,7 @@ public function testCachePageCLIRequest(): void
 
         $cachedResponse = $pageCache->get($request, new Response($this->appConfig));
 
-        $this->assertNull($cachedResponse);
+        $this->assertNotInstanceOf(ResponseInterface::class, $cachedResponse);
     }
 
     public function testUnserializeError(): void

tests/system/Filters/CorsTest.php

@@ -102,7 +102,7 @@ public function testBeforeDoesNothingWhenCliRequest(): void
 
         $return = $this->cors->before($cliRequest);
 
-        $this->assertNull($return);
+        $this->assertNotInstanceOf(ResponseInterface::class, $return);
     }
 
     private function assertHeader(string $name, string $value): void

tests/system/HTTP/Files/FileCollectionTest.php

@@ -524,7 +524,7 @@ public function testFileNoExistSingleFile(): void
 
         $collection = new FileCollection();
         $file       = $collection->getFile('fileuser');
-        $this->assertNull($file);
+        $this->assertNotInstanceOf(UploadedFile::class, $file);
     }
 
     public function testFileReturnValidMultipleFiles(): void
@@ -686,7 +686,7 @@ public function testDoesntHaveFile(): void
         $collection = new FileCollection();
 
         $this->assertFalse($collection->hasFile('my-form.detailz.avatars.0'));
-        $this->assertNull($collection->getFile('my-form.detailz.avatars.0'));
+        $this->assertNotInstanceOf(UploadedFile::class, $collection->getFile('my-form.detailz.avatars.0'));
     }
 
     public function testGetFileMultipleHasNoFile(): void

tests/system/HTTP/ResponseTest.php

@@ -495,7 +495,7 @@ public function testVagueDownload(): void
 
         $actual = $response->download();
 
-        $this->assertNull($actual);
+        $this->assertNotInstanceOf(DownloadResponse::class, $actual);
     }
 
     public function testPretendMode(): void

tests/system/Images/GDHandlerTest.php

@@ -411,7 +411,7 @@ public function testImageConvert(): void
         $this->handler->withFile($this->origin . 'ci-logo.jpeg');
         $this->handler->convert(IMAGETYPE_PNG);
         $this->handler->save($this->start . 'work/ci-logo.png');
-        $this->assertSame(exif_imagetype($this->start . 'work/ci-logo.png'), IMAGETYPE_PNG);
+        $this->assertSame(IMAGETYPE_PNG, exif_imagetype($this->start . 'work/ci-logo.png'));
     }
 
     public function testImageConvertPngToWebp(): void
@@ -420,7 +420,7 @@ public function testImageConvertPngToWebp(): void
         $this->handler->convert(IMAGETYPE_WEBP);
         $saved = $this->start . 'work/rocket.webp';
         $this->handler->save($saved);
-        $this->assertSame(exif_imagetype($saved), IMAGETYPE_WEBP);
+        $this->assertSame(IMAGETYPE_WEBP, exif_imagetype($saved));
     }
 
     public function testImageReorientLandscape(): void

tests/system/Images/ImageMagickHandlerTest.php

@@ -447,10 +447,10 @@
         $this->handler->withFile($this->origin . 'ci-logo.jpeg');
         $this->handler->convert(IMAGETYPE_PNG);
         $this->handler->save($this->root . 'ci-logo.png');
-        $this->assertSame(exif_imagetype($this->root . 'ci-logo.png'), IMAGETYPE_PNG);
+        $this->assertSame(IMAGETYPE_PNG, exif_imagetype($this->root . 'ci-logo.png'));
     }
 
     public function testImageReorientLandscape(): void
     {
         for ($i = 0; $i <= 8; $i++) {
             $source = $this->origin . 'EXIFsamples/landscape_' . $i . '.jpg';
@@ -469,7 +469,7 @@
         }
     }
 
     public function testImageReorientPortrait(): void
     {
         for ($i = 0; $i <= 8; $i++) {
             $source = $this->origin . 'EXIFsamples/portrait_' . $i . '.jpg';