Add test of rustdoc sort order for stable vs unstable item

Author: dtolnay

tests/rustdoc/stability.rs

@@ -2,6 +2,14 @@
 
 #![unstable(feature = "test", issue = "none")]
 
+// @has stability/index.html
+// @has - '//ul[@class="item-table"]/li[1]//a' Unstable
+// @has - '//ul[@class="item-table"]/li[2]//a' AaStable
+// @has - '//ul[@class="item-table"]/li[3]//a' ZzStable
+
+#[stable(feature = "rust2", since = "2.2.2")]
+pub struct AaStable;
+
 pub struct Unstable {
     // @has stability/struct.Unstable.html \
     //      '//span[@class="item-info"]//div[@class="stab unstable"]' \
@@ -10,3 +18,6 @@ pub struct Unstable {
     pub foo: u32,
     pub bar: u32,
 }
+
+#[stable(feature = "rust2", since = "2.2.2")]
+pub struct ZzStable;