Add tests for no-hidden-lines codeblock attribute

tests/rustdoc/no-hidden-lines-codeblock-format.codeblock-non-raw.html

@@ -0,0 +1,8 @@
+<code><span class="macro">macro_rules! </span>test {
+    (# a,##b,###c) =&gt; {}
+}
+
+<span class="macro">test!</span>(
+    #b,
+    ##c
+);</code>

tests/rustdoc/no-hidden-lines-codeblock-format.codeblock.html

@@ -0,0 +1,9 @@
+<code><span class="macro">macro_rules! </span>test {
+    (# a,##b,###c) =&gt; {}
+}
+
+<span class="macro">test!</span>(
+    # a,
+    ##b,
+    ###c
+);</code>

tests/rustdoc/no-hidden-lines-codeblock-format.rs

@@ -0,0 +1,54 @@
+// Test that the `no_hidden_lines` codeblock attribute prevents lines starting with `#` to
+// be stripped.
+
+#![crate_name = "foo"]
+
+// @has 'foo/index.html'
+// @matches - '//*[@class="rust rust-example-rendered"]/code' '\(\s+# a,\s+##b,\s+###c\s+\);'
+// @snapshot 'codeblock' - '//*[@class="rust rust-example-rendered"]/code'
+
+//! ```rust,no_hidden_lines
+//! macro_rules! test {
+//!     (# a,##b,###c) => {}
+//! }
+//!
+//! test!(
+//!     # a,
+//!     ##b,
+//!     ###c
+//! );
+//! ```
+
+// @has 'foo/fn.foo.html'
+// @matches - '//*[@class="rust rust-example-rendered"]/code' '\(\s+#b,\s+##c\s+\);'
+// @snapshot 'codeblock-non-raw' - '//*[@class="rust rust-example-rendered"]/code'
+
+/// ```
+/// macro_rules! test {
+///     (# a,##b,###c) => {}
+/// }
+///
+/// test!(
+///     # a,
+///     ##b,
+///     ###c
+/// );
+/// ```
+pub fn foo() {}
+
+// Testing that `raw` means that it is a rust code block by default.
+// @has 'foo/fn.bar.html'
+// @matches - '//*[@class="rust rust-example-rendered"]/code' '\(\s+#a,\s+##b,\s+###c\s+\);'
+
+/// ```no_hidden_lines
+/// macro_rules! test {
+///     (#a,##b,###c) => {}
+/// }
+///
+/// test!(
+///     #a,
+///     ##b,
+///     ###c
+/// );
+/// ```
+pub fn bar() {}