diff --git a/tests/rendered_output.rs b/tests/rendered_output.rs
index 591634db..7a726f87 100644
--- a/tests/rendered_output.rs
+++ b/tests/rendered_output.rs
@@ -328,26 +328,6 @@ fn example_book_can_build() {
     md.build().unwrap();
 }
 
-#[test]
-fn by_default_mdbook_use_index_preprocessor_to_convert_readme_to_index() {
-    let temp = DummyBook::new().build().unwrap();
-    let mut cfg = Config::default();
-    cfg.set("book.src", "src2")
-        .expect("Couldn't set config.book.src to \"src2\".");
-    let md = MDBook::load_with_config(temp.path(), cfg).unwrap();
-    md.build().unwrap();
-
-    let first_index = temp.path().join("book").join("toc.js");
-    let expected_strings = vec![
-        r#"href="first/index.html""#,
-        r#"href="second/index.html""#,
-        "1st README",
-        "2nd README",
-    ];
-    assert_contains_strings(&first_index, &expected_strings);
-    assert_doesnt_contain_strings(&first_index, &["README.html", "Second README"]);
-}
-
 #[test]
 fn first_chapter_is_copied_as_index_even_if_not_first_elem() {
     let temp = DummyBook::new().build().unwrap();
diff --git a/tests/testsuite/index.rs b/tests/testsuite/index.rs
new file mode 100644
index 00000000..0555cc63
--- /dev/null
+++ b/tests/testsuite/index.rs
@@ -0,0 +1,38 @@
+//! Tests for the index preprocessor.
+
+use crate::prelude::*;
+
+// Checks basic README to index.html conversion.
+#[test]
+fn readme_to_index() {
+    let mut test = BookTest::from_dir("index/basic_readme");
+    test.check_main_file(
+        "book/index.html",
+        str![[r##"<h1 id="intro"><a class="header" href="#intro">Intro</a></h1>"##]],
+    )
+    .check_main_file(
+        "book/first/index.html",
+        str![[r##"<h1 id="first"><a class="header" href="#first">First</a></h1>"##]],
+    )
+    .check_main_file(
+        "book/second/index.html",
+        str![[r##"<h1 id="second"><a class="header" href="#second">Second</a></h1>"##]],
+    )
+    .check_toc_js(str![[r#"
+<ol class="chapter">
+<li class="chapter-item expanded affix ">
+<a href="index.html">Intro</a>
+</li>
+<li class="chapter-item expanded ">
+<a href="first/index.html">
+<strong aria-hidden="true">1.</strong> First</a>
+</li>
+<li class="chapter-item expanded ">
+<a href="second/index.html">
+<strong aria-hidden="true">2.</strong> Second</a>
+</li>
+</ol>
+"#]]);
+    assert!(test.dir.join("book/index.html").exists());
+    assert!(!test.dir.join("book/README.html").exists());
+}
diff --git a/tests/testsuite/index/basic_readme/book.toml b/tests/testsuite/index/basic_readme/book.toml
new file mode 100644
index 00000000..271699ca
--- /dev/null
+++ b/tests/testsuite/index/basic_readme/book.toml
@@ -0,0 +1,2 @@
+[book]
+title = "basic_readme"
diff --git a/tests/testsuite/index/basic_readme/src/README.md b/tests/testsuite/index/basic_readme/src/README.md
new file mode 100644
index 00000000..1e0981f1
--- /dev/null
+++ b/tests/testsuite/index/basic_readme/src/README.md
@@ -0,0 +1 @@
+# Intro
diff --git a/tests/testsuite/index/basic_readme/src/SUMMARY.md b/tests/testsuite/index/basic_readme/src/SUMMARY.md
new file mode 100644
index 00000000..fd4cbac2
--- /dev/null
+++ b/tests/testsuite/index/basic_readme/src/SUMMARY.md
@@ -0,0 +1,6 @@
+# Summary
+
+[Intro](./README.md)
+
+- [First](first/README)
+- [Second](second/Readme.md)
diff --git a/tests/testsuite/index/basic_readme/src/first/README b/tests/testsuite/index/basic_readme/src/first/README
new file mode 100644
index 00000000..f6758542
--- /dev/null
+++ b/tests/testsuite/index/basic_readme/src/first/README
@@ -0,0 +1 @@
+# First
diff --git a/tests/testsuite/index/basic_readme/src/second/Readme.md b/tests/testsuite/index/basic_readme/src/second/Readme.md
new file mode 100644
index 00000000..64e2582b
--- /dev/null
+++ b/tests/testsuite/index/basic_readme/src/second/Readme.md
@@ -0,0 +1 @@
+# Second
diff --git a/tests/testsuite/main.rs b/tests/testsuite/main.rs
index d273b992..6141c4f7 100644
--- a/tests/testsuite/main.rs
+++ b/tests/testsuite/main.rs
@@ -6,6 +6,7 @@ mod book_test;
 mod build;
 mod cli;
 mod includes;
+mod index;
 
 mod prelude {
     pub use crate::book_test::BookTest;