Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

crates/nu-command/tests/commands/mkdir.rs

@@ -0,0 +1,84 @@
+use nu_test_support::fs::files_exist_at;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, pipeline};
+use std::path::Path;
+
+#[test]
+fn creates_directory() {
+    Playground::setup("mkdir_test_1", |dirs, _| {
+        nu!(
+            cwd: dirs.test(),
+            "mkdir my_new_directory"
+        );
+
+        let expected = dirs.test().join("my_new_directory");
+
+        assert!(expected.exists());
+    })
+}
+
+#[test]
+fn accepts_and_creates_directories() {
+    Playground::setup("mkdir_test_2", |dirs, _| {
+        nu!(
+            cwd: dirs.test(),
+            "mkdir dir_1 dir_2 dir_3"
+        );
+
+        assert!(files_exist_at(
+            vec![Path::new("dir_1"), Path::new("dir_2"), Path::new("dir_3")],
+            dirs.test()
+        ));
+    })
+}
+
+#[test]
+fn creates_intermediary_directories() {
+    Playground::setup("mkdir_test_3", |dirs, _| {
+        nu!(
+            cwd: dirs.test(),
+            "mkdir some_folder/another/deeper_one"
+        );
+
+        let expected = dirs.test().join("some_folder/another/deeper_one");
+
+        assert!(expected.exists());
+    })
+}
+
+#[test]
+fn create_directory_two_parents_up_using_multiple_dots() {
+    Playground::setup("mkdir_test_4", |dirs, sandbox| {
+        sandbox.within("foo").mkdir("bar");
+
+        nu!(
+            cwd: dirs.test().join("foo/bar"),
+            "mkdir .../boo"
+        );
+
+        let expected = dirs.test().join("boo");
+
+        assert!(expected.exists());
+    })
+}
+
+#[test]
+fn show_created_paths() {
+    Playground::setup("mkdir_test_2", |dirs, _| {
+        let actual = nu!(
+         cwd: dirs.test(),
+         pipeline(
+             r#"
+                 mkdir -s dir_1 dir_2 dir_3
+                 | length
+             "#
+        ));
+
+        assert!(files_exist_at(
+            vec![Path::new("dir_1"), Path::new("dir_2"), Path::new("dir_3")],
+            dirs.test()
+        ));
+
+        assert_eq!(actual.out, "3");
+    })
+}