Migrate process_the_dummy_book to BookTest

tests/custom_preprocessors.rs

@@ -56,13 +56,3 @@ fn ask_the_preprocessor_to_blow_up() {
         )
     );
 }
-
-#[test]
-fn process_the_dummy_book() {
-    let dummy_book = DummyBook::new();
-    let temp = dummy_book.build().unwrap();
-    let mut md = MDBook::load(temp.path()).unwrap();
-    md.with_preprocessor(example());
-
-    md.build().unwrap();
-}

tests/testsuite/preprocessor.rs

@@ -40,3 +40,15 @@ fn runs_preprocessors() {
     assert_eq!(inner.run_count, 1);
     assert_eq!(inner.rendered_with, ["html"]);
 }
+
+// No-op preprocessor works.
+#[test]
+fn nop_preprocessor() {
+    BookTest::from_dir("preprocessor/nop_preprocessor").run("build", |cmd| {
+        cmd.expect_stdout(str![[""]]).expect_stderr(str![[r#"
+[TIMESTAMP] [INFO] (mdbook::book): Book building has started
+[TIMESTAMP] [INFO] (mdbook::book): Running the html backend
+
+"#]]);
+    });
+}

tests/testsuite/preprocessor/nop_preprocessor/book.toml

@@ -0,0 +1,2 @@
+[preprocessor.nop-preprocessor]
+command = "cargo run --quiet --example nop-preprocessor --"