Add two tests

Author: jstasiak

tests/testsuite/build.rs

@@ -4989,3 +4989,32 @@ fn reduced_reproduction_8249() {
     p.cargo("check").run();
     p.cargo("check").run();
 }
+
+#[cargo_test]
+fn target_directory_is_excluded_from_backups() {
+    let p = project()
+        .file("Cargo.toml", &basic_bin_manifest("foo"))
+        .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
+        .build();
+
+    p.cargo("build").run();
+    let cachedir_tag = p.target_debug_dir().join("CACHEDIR.TAG");
+    assert!(cachedir_tag.is_file());
+    assert!(fs::read_to_string(&cachedir_tag)
+        .unwrap()
+        .starts_with("Signature: 8a477f597d28d172789f06886806bc55"));
+}
+
+#[cargo_test]
+fn target_directory_is_not_excluded_from_backups_if_it_already_exists() {
+    let p = project()
+        .file("Cargo.toml", &basic_bin_manifest("foo"))
+        .file("src/foo.rs", &main_file(r#""i am foo""#, &[]))
+        .build();
+
+    let cachedir_tag = p.target_debug_dir().join("CACHEDIR.TAG");
+    p.cargo("build").run();
+    fs::remove_file(&cachedir_tag).unwrap();
+    p.cargo("build").run();
+    assert!(!&cachedir_tag.is_file());
+}