Revert "skip test while snapshot downloader cannot handle downgrades (#…

…3314)" (#3385)

* Revert "skip test while snapshot downloader cannot handle downgrades (#3314)"

This reverts commit a8d8fce.

* Update upgrade_test.go

internal/pkg/agent/application/upgrade/upgrade.go

@@ -118,10 +118,7 @@ func (u *Upgrader) Upgrade(ctx context.Context, version string, sourceURI string
 		u.log.Errorw("Unable to clean downloads before update", "error.message", err, "downloads.path", paths.Downloads())
 	}
 
-	if sourceURI != "" {
-		sourceURI = u.settings.SourceURI
-	}
-
+	sourceURI = u.sourceURI(sourceURI)
 	archivePath, err := u.downloadArtifact(ctx, version, sourceURI, skipVerifyOverride, skipDefaultPgp, pgpBytes...)
 	if err != nil {
 		// Run the same pre-upgrade cleanup task to get rid of any newly downloaded files
@@ -217,6 +214,14 @@ func (u *Upgrader) Ack(ctx context.Context, acker acker.Acker) error {
 	return saveMarker(marker)
 }
 
+func (u *Upgrader) sourceURI(retrievedURI string) string {
+	if retrievedURI != "" {
+		return retrievedURI
+	}
+
+	return u.settings.SourceURI
+}
+
 func rollbackInstall(ctx context.Context, log *logger.Logger, hash string) {
 	os.RemoveAll(filepath.Join(paths.Data(), fmt.Sprintf("%s-%s", agentName, hash)))
 	_ = ChangeSymlink(ctx, log, release.ShortCommit())

testing/integration/upgrade_test.go

@@ -227,15 +227,12 @@ func TestStandaloneUpgrade(t *testing.T) {
 	}
 }
 
-func TestStandaloneDowngradeWithGPGFallback(t *testing.T) {
+func TestStandaloneUpgradeWithGPGFallback(t *testing.T) {
 	define.Require(t, define.Requirements{
 		Local: false, // requires Agent installation
 		Sudo:  true,  // requires Agent installation
 	})
 
-	t.Skip("snapshot downloader has a bug which break this test between releases: " +
-		"https://github.com/elastic/elastic-agent/issues/3313")
-
 	minVersion := version_8_10_0_SNAPSHOT
 	fromVersion, err := version.ParseVersion(define.Version())
 	require.NoError(t, err)