Add tests for ensuring docblock headings.

src/test/rustdoc/issue-89309-heading-levels.rs

@@ -0,0 +1,29 @@
+#![crate_name = "foo"]
+
+// @has foo/trait.Read.html
+// @has - '//h2' 'Trait examples'
+/// # Trait examples
+pub trait Read {
+    // @has - '//h5' 'Function examples'
+    /// # Function examples
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, ()>;
+}
+
+pub struct Foo;
+
+// @has foo/struct.Foo.html
+impl Foo {
+    // @has - '//h5' 'Implementation header'
+    /// # Implementation header
+    pub fn bar(&self) -> usize {
+        1
+    }
+}
+
+impl Read for Foo {
+    // @has - '//h5' 'Trait implementation header'
+    /// # Trait implementation header
+    fn read(&mut self, buf: &mut [u8]) -> Result<usize, ()> {
+        Ok(1)
+    }
+}