Migrate missing_backends_are_fatal to BookTest

tests/alternative_backends.rs

@@ -6,15 +6,6 @@ use std::fs;
 use std::path::Path;
 use tempfile::{Builder as TempFileBuilder, TempDir};
 
-#[test]
-fn missing_backends_are_fatal() {
-    let (md, _temp) = dummy_book_with_backend("missing", "trduyvbhijnorgevfuhn", false);
-    let got = md.build();
-    assert!(got.is_err());
-    let error_message = got.err().unwrap().to_string();
-    assert_eq!(error_message, "Rendering failed");
-}
-
 #[test]
 fn missing_optional_backends_are_not_fatal() {
     let (md, _temp) = dummy_book_with_backend("missing", "trduyvbhijnorgevfuhn", true);

tests/testsuite/renderer.rs

@@ -72,3 +72,22 @@ fn failing_command() {
 "#]]);
         });
 }
+
+// Renderer command is missing.
+#[test]
+fn missing_renderer() {
+    BookTest::from_dir("renderer/missing_renderer").run("build", |cmd| {
+        cmd.expect_failure()
+            .expect_stdout(str![[""]])
+            .expect_stderr(str![[r#"
+[TIMESTAMP] [INFO] (mdbook::book): Book building has started
+[TIMESTAMP] [INFO] (mdbook::book): Running the missing backend
+[TIMESTAMP] [INFO] (mdbook::renderer): Invoking the "missing" renderer
+[TIMESTAMP] [ERROR] (mdbook::renderer): The command `trduyvbhijnorgevfuhn` wasn't found, is the "missing" backend installed? If you want to ignore this error when the "missing" backend is not installed, set `optional = true` in the `[output.missing]` section of the book.toml configuration file.
+[TIMESTAMP] [ERROR] (mdbook::utils): Error: Rendering failed
+[TIMESTAMP] [ERROR] (mdbook::utils): [TAB]Caused By: Unable to start the backend
+[TIMESTAMP] [ERROR] (mdbook::utils): [TAB]Caused By: [NOT_FOUND]
+
+"#]]);
+    });
+}

tests/testsuite/renderer/missing_renderer/book.toml

@@ -0,0 +1,3 @@
+[output.missing]
+command = "trduyvbhijnorgevfuhn"
+