Add example for CLI tests with temporary directories and setting the current working directory (CWD)

src/tutorial/testing.md

@@ -472,7 +472,7 @@ at the end of the function,
 the actual temporary file will automatically get deleted.
 
 ```rust,ignore
-{{#include testing/tests/cli.rs:17:32}}
+{{#include testing/tests/cli.rs:17:30}}
 ```
 
 <aside class="exercise">
@@ -483,6 +483,31 @@ Adjust the program as needed.
 
 </aside>
 
+## Executing tests in a temporary directory
+
+To fully control the behavior of your CLI app, you can use
+`assert_fs::TempDir::new()` to create a temporary directory.
+This is useful when you need to read and write
+multiple directories or files. You can also use it as the
+current working directory (CWD) when executing your CLI app,
+ensuring test results are consistent and don't interfere with
+other, unrelated files.
+
+Temporary directories allow you to create multiple child
+directories and files within them, enabling more advanced
+test cases. Just like for single temporary files,
+all nested files and directories within temporary directories
+are also cleaned up after the test is completed.
+
+```rust,ignore
+{{#include testing/tests/cli.rs:32:56}}
+```
+
+You now know the core features of the crates `assert_cmd`,
+`assert_fs` and `predicates` and are ready to start testing
+your own CLI apps. Feel free to check out their documentation
+to find more useful features.
+
 ## What to test?
 
 While it can certainly be fun to write integration tests,

src/tutorial/testing/tests/cli.rs

@@ -28,3 +28,29 @@ fn find_content_in_file() -> Result<(), Box<dyn std::error::Error>> {
 
     Ok(())
 }
+
+#[test]
+fn find_content_in_file_of_tmp_dir() -> Result<(), Box<dyn std::error::Error>> {
+    let cwd = assert_fs::TempDir::new()?;
+
+    let child_dir = cwd.child("nested/child_dir");
+    let child_file = child_dir.child("sample.txt");
+
+    child_file.write_str("The first\ntest file.\nLast line of first file.")?;
+
+    // Files can be nested several levels within the temporary directory
+    assert!(child_file.path().ends_with("nested/child_dir/sample.txt"));
+
+    cargo_bin_cmd!("grrs")
+        // Execute in the temporary directory
+        .current_dir(cwd.path())
+        .arg("first")
+        .arg(child_file.path())
+        .assert()
+        .success()
+        .stdout(predicate::str::contains(
+            "The first\nLast line of first file.",
+        ));
+
+    Ok(())
+}