Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

crates/nu-command/tests/commands/path/expand.rs

@@ -0,0 +1,78 @@
+use nu_test_support::fs::Stub::EmptyFile;
+use nu_test_support::playground::Playground;
+use nu_test_support::{nu, pipeline};
+
+use std::path::PathBuf;
+
+#[test]
+fn expands_path_with_dot() {
+    Playground::setup("path_expand_1", |dirs, sandbox| {
+        sandbox
+            .within("menu")
+            .with_files(vec![EmptyFile("spam.txt")]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                echo "menu/./spam.txt" 
+                | path expand
+            "#
+        ));
+
+        let expected = dirs.test.join("menu").join("spam.txt");
+        assert_eq!(PathBuf::from(actual.out), expected);
+    })
+}
+
+#[test]
+fn expands_path_with_double_dot() {
+    Playground::setup("path_expand_2", |dirs, sandbox| {
+        sandbox
+            .within("menu")
+            .with_files(vec![EmptyFile("spam.txt")]);
+
+        let actual = nu!(
+            cwd: dirs.test(), pipeline(
+            r#"
+                echo "menu/../menu/spam.txt" 
+                | path expand
+            "#
+        ));
+
+        let expected = dirs.test.join("menu").join("spam.txt");
+        assert_eq!(PathBuf::from(actual.out), expected);
+    })
+}
+
+#[cfg(windows)]
+mod windows {
+    use super::*;
+
+    #[test]
+    fn expands_path_with_tilde_backward_slash() {
+        Playground::setup("path_expand_2", |dirs, _| {
+            let actual = nu!(
+                cwd: dirs.test(), pipeline(
+                r#"
+                    echo "~\tmp.txt" | path expand
+                "#
+            ));
+
+            assert!(!PathBuf::from(actual.out).starts_with("~"));
+        })
+    }
+
+    #[test]
+    fn win_expands_path_with_tilde_forward_slash() {
+        Playground::setup("path_expand_2", |dirs, _| {
+            let actual = nu!(
+                cwd: dirs.test(), pipeline(
+                r#"
+                    echo "~/tmp.txt" | path expand
+                "#
+            ));
+
+            assert!(!PathBuf::from(actual.out).starts_with("~"));
+        })
+    }
+}