Do not change any digest when the environment version changes

The digests should be a direct result of the source digest. Only cache
related values should change.

lib/sprockets/asset.rb

@@ -130,11 +130,13 @@ def environment_version
 
     # Public: Returns String hexdigest of source.
     def hexdigest
-      DigestUtils.pack_hexdigest(environment_version + digest)
+      DigestUtils.pack_hexdigest(digest)
     end
 
     # Pubic: ETag String of Asset.
-    alias_method :etag, :hexdigest
+    def etag
+      DigestUtils.pack_hexdigest(environment_version + digest)
+    end
 
     # Public: Returns String base64 digest of source.
     def base64digest

test/test_environment.rb

@@ -723,13 +723,45 @@ def setup
   test "changing version changes the digest_path of the asset" do
     old_asset_digest = @env["gallery.js"].digest_path
     @env.version = 'v2'
-    assert old_asset_digest != @env["gallery.js"].digest_path
+    refute_equal old_asset_digest, @env["gallery.js"].digest_path
   end
 
-  test "changing version changes the digest of the asset" do
-    old_asset_digest = @env["gallery.js"].hexdigest
+  test "changing version changes the etag of the asset" do
+    old_asset_etag = @env["gallery.js"].etag
     @env.version = 'v2'
-    assert old_asset_digest != @env["gallery.js"].hexdigest
+    refute_equal old_asset_etag, @env["gallery.js"].etag
+  end
+
+  test "changing version does not changes the digest of the asset" do
+    old_asset_digest = @env["gallery.js"].digest
+
+    @env.version = 'v2'
+
+    assert_equal old_asset_digest, @env["gallery.js"].digest
+  end
+
+  test "changing version does not changes the hexdigest of the asset" do
+    old_asset_hexdigest = @env["gallery.js"].hexdigest
+
+    @env.version = 'v2'
+
+    assert_equal old_asset_hexdigest, @env["gallery.js"].hexdigest
+  end
+
+  test "changing version does not changes the base64digest of the asset" do
+    old_asset_base64digest = @env["gallery.js"].base64digest
+
+    @env.version = 'v2'
+
+    assert_equal old_asset_base64digest, @env["gallery.js"].base64digest
+  end
+
+  test "changing version does not changes the integrity of the asset" do
+    old_asset_integrity = @env["gallery.js"].integrity
+
+    @env.version = 'v2'
+
+    assert_equal old_asset_integrity, @env["gallery.js"].integrity
   end
 
   test "bundled asset is stale if its mtime is updated or deleted" do