Add test to check that renderer utilizes PATH

Author: krishanjmistry

tests/testsuite/renderer.rs

@@ -75,6 +75,48 @@ fn failing_command() {
         });
 }
 
+// Test that renderer utilizes PATH to find mdbook-FOO executables.
+#[test]
+fn renderer_utilizes_path() {
+    let mut test = BookTest::init(|_| {});
+    test.rust_program(
+        "custom_directory/mdbook-in_path",
+        r#"
+            fn main() {
+                // Read from stdin to avoid random pipe failures on Linux.
+                use std::io::Read;
+                let mut s = String::new();
+                std::io::stdin().read_to_string(&mut s).unwrap();
+                println!("Hello World!");
+            }
+            "#,
+    )
+    .change_file(
+        "book.toml",
+        "[output.in_path]\n\
+",
+    );
+    let custom_directory_path = test
+        .dir
+        .join("custom_directory")
+        .to_str()
+        .unwrap()
+        .to_string();
+    test.run("build", |cmd| {
+        cmd.env("PATH", format!("$PATH:{}", custom_directory_path));
+        cmd.expect_stdout(str![[r#"
+Hello World!
+
+"#]])
+            .expect_stderr(str![[r#"
+[TIMESTAMP] [INFO] (mdbook::book): Book building has started
+[TIMESTAMP] [INFO] (mdbook::book): Running the in_path backend
+[TIMESTAMP] [INFO] (mdbook::renderer): Invoking the "in_path" renderer
+
+"#]]);
+    });
+}
+
 // Renderer command is missing.
 #[test]
 fn missing_renderer() {