Migrate able_to_include_playground_files_in_chapters to BookTest

tests/rendered_output.rs

@@ -334,22 +334,6 @@ fn check_link_target_fallback() {
     );
 }
 
-/// This makes sure you can include a Rust file with `{{#playground example.rs}}`.
-/// Specification is in `guide/src/format/rust.md`
-#[test]
-fn able_to_include_playground_files_in_chapters() {
-    let temp = DummyBook::new().build().unwrap();
-    let md = MDBook::load(temp.path()).unwrap();
-    md.build().unwrap();
-
-    let second = temp.path().join("book/second.html");
-
-    let playground_strings = &[r#"class="playground""#, r#"println!("Hello World!");"#];
-
-    assert_contains_strings(&second, playground_strings);
-    assert_doesnt_contain_strings(&second, &["{{#playground example.rs}}"]);
-}
-
 #[test]
 fn example_book_can_build() {
     let example_book_dir = dummy_book::new_copy_of_example_book().unwrap();

tests/testsuite/includes.rs

@@ -68,3 +68,19 @@ Around the world, around the world</p>
 "#]],
         );
 }
+
+// Checks the behavior of `{{#playground}}` include.
+#[test]
+fn playground_include() {
+    BookTest::from_dir("includes/all_includes")
+        .check_main_file("book/playground.html",
+            str![[r##"
+<h1 id="playground-includes"><a class="header" href="#playground-includes">Playground Includes</a></h1>
+<pre><pre class="playground"><code class="language-rust">fn main() {
+    println!("Hello World!");
+<span class="boring">
+</span><span class="boring">   // You can even hide lines! :D
+</span><span class="boring">  println!("I am hidden! Expand the code snippet to see me");
+</span>}</code></pre></pre>
+"##]]);
+}