stdlib: refactor into a multi-module library (#8815)

crates/nu-std/tests/test_std.nu

@@ -0,0 +1,24 @@
+use std
+
+export def test_path_add [] {
+    use std "assert equal"
+
+    with-env [PATH []] {
+        assert equal $env.PATH []
+
+        std path add "/foo/"
+        assert equal $env.PATH ["/foo/"]
+
+        std path add "/bar/" "/baz/"
+        assert equal $env.PATH ["/bar/", "/baz/", "/foo/"]
+
+        let-env PATH = []
+
+        std path add "foo"
+        std path add "bar" "baz" --append
+        assert equal $env.PATH ["foo", "bar", "baz"]
+
+        assert equal (std path add "fooooo" --ret) ["fooooo", "foo", "bar", "baz"]
+        assert equal $env.PATH ["fooooo", "foo", "bar", "baz"]
+    }
+}