Tested MDBook::init with custom args

tests/init.rs

@@ -21,3 +21,23 @@ fn run_mdbook_init() {
         assert!(temp.path().join(file).exists(), "{} doesn't exist", file);
     }
 }
+
+#[test]
+fn run_mdbook_init_with_custom_args() {
+    let created_files = vec!["out", "in", "in/SUMMARY.md", "in/chapter_1.md"];
+
+    let temp = TempDir::new("mdbook").unwrap();
+    for file in &created_files {
+        assert!(!temp.path().join(file).exists());
+    }
+
+    let mut md = MDBook::new(temp.path())
+        .with_source("in")
+        .with_destination("out");
+
+    md.init().unwrap();
+
+    for file in &created_files {
+        assert!(temp.path().join(file).exists(), "{} doesn't exist", file);
+    }
+}