minor symfony#58011 [HttpKernel] Improve and add tests for Last-Modified computation with ESI responses (mpdude)

This PR was merged into the 6.4 branch.

Discussion
----------

[HttpKernel] Improve and add tests for `Last-Modified` computation with ESI responses

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Issues        |
| License       | MIT

This PR slightly improves the test cases for symfony#42355 (which fixed symfony#41666).

It adds two tests for the cases where `Last-Modified` should _not_ be added,
and updates the existing test to make it more obvious that we only look at
the existence of `Last-Modified` headers, whereas the `ETag` is not
relevant.

Commits
-------

40d5455 Improve and add tests for Last-Modified computation with ESI responses

Author: nicolas-grekas

src/Symfony/Component/HttpKernel/Tests/HttpCache/ResponseCacheStrategyTest.php

@@ -138,22 +138,48 @@ public function testLastModifiedIsMergedWithEmbeddedResponse()
     {
         $cacheStrategy = new ResponseCacheStrategy();
 
+        $mainResponse = new Response();
+        $mainResponse->setLastModified(new \DateTimeImmutable('-2 hour'));
+
         $embeddedDate = new \DateTimeImmutable('-1 hour');
+        $embeddedResponse = new Response();
+        $embeddedResponse->setLastModified($embeddedDate);
 
-        // This master response uses the "validation" model
-        $masterResponse = new Response();
-        $masterResponse->setLastModified(new \DateTimeImmutable('-2 hour'));
-        $masterResponse->setEtag('foo');
+        $cacheStrategy->add($embeddedResponse);
+        $cacheStrategy->update($mainResponse);
+
+        $this->assertTrue($mainResponse->headers->has('Last-Modified'));
+        $this->assertSame($embeddedDate->getTimestamp(), $mainResponse->getLastModified()->getTimestamp());
+    }
+
+    public function testLastModifiedIsRemovedWhenEmbeddedResponseHasNoLastModified()
+    {
+        $cacheStrategy = new ResponseCacheStrategy();
+
+        $mainResponse = new Response();
+        $mainResponse->setLastModified(new \DateTimeImmutable('-2 hour'));
 
-        // Embedded response uses "expiry" model
         $embeddedResponse = new Response();
-        $embeddedResponse->setLastModified($embeddedDate);
+
         $cacheStrategy->add($embeddedResponse);
+        $cacheStrategy->update($mainResponse);
+
+        $this->assertFalse($mainResponse->headers->has('Last-Modified'));
+    }
 
-        $cacheStrategy->update($masterResponse);
+    public function testLastModifiedIsNotAddedWhenMainResponseHasNoLastModified()
+    {
+        $cacheStrategy = new ResponseCacheStrategy();
 
-        $this->assertTrue($masterResponse->isValidateable());
-        $this->assertSame($embeddedDate->getTimestamp(), $masterResponse->getLastModified()->getTimestamp());
+        $mainResponse = new Response();
+
+        $embeddedResponse = new Response();
+        $embeddedResponse->setLastModified(new \DateTimeImmutable('-2 hour'));
+
+        $cacheStrategy->add($embeddedResponse);
+        $cacheStrategy->update($mainResponse);
+
+        $this->assertFalse($mainResponse->headers->has('Last-Modified'));
     }
 
     public function testMainResponseIsNotCacheableWhenEmbeddedResponseIsNotCacheable()