Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

crates/nu-command/tests/commands/random/chars.rs

@@ -0,0 +1,14 @@
+use nu_test_support::{nu, pipeline};
+
+#[test]
+fn generates_chars_of_specified_length() {
+    let actual = nu!(
+        cwd: ".", pipeline(
+        r#"
+        random chars -l 15 | size | get chars
+        "#
+    ));
+
+    let result = actual.out;
+    assert_eq!(result, "15");
+}