Add test for empty impl blocks

Author: GuillaumeGomez

src/test/rustdoc/empty-impl-block.rs

@@ -0,0 +1,20 @@
+#![crate_name = "foo"]
+
+// @has 'foo/struct.Foo.html'
+pub struct Foo;
+
+// @has - '//*[@class="docblock"]' 'Hello empty impl block!'
+// @has - '//*[@class="item-info"]' 'This impl block contains no items.'
+/// Hello empty impl block!
+impl Foo {}
+// We ensure that this empty impl block without doc isn't rendered.
+// @count - '//*[@class="impl has-srclink"]' 'impl Foo' 1
+impl Foo {}
+
+// Just to ensure that empty trait impl blocks are rendered.
+pub struct Another;
+pub trait Bar {}
+
+// @has 'foo/struct.Another.html'
+// @has - '//h3[@class="code-header in-band"]' 'impl Bar for Another'
+impl Bar for Another {}