Command tests (#922)

* WIP command tests

* Finish marking todo tests

* update

* update

* Windows cd test ignoring

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

@@ -0,0 +1,96 @@
+use nu_test_support::nu;
+
+#[test]
+fn which_ls() {
+    let actual = nu!(
+        cwd: ".",
+        "which ls | get path | str trim"
+    );
+
+    assert_eq!(actual.out, "Nushell built-in command");
+}
+
+#[test]
+fn which_alias_ls() {
+    let actual = nu!(
+        cwd: ".",
+        "alias ls = ls -a; which ls | get path | str trim"
+    );
+
+    assert_eq!(actual.out, "Nushell alias: ls -a");
+}
+
+#[test]
+fn which_def_ls() {
+    let actual = nu!(
+        cwd: ".",
+        "def ls [] {echo def}; which ls | get path | str trim"
+    );
+
+    assert_eq!(actual.out, "Nushell custom command");
+}
+
+#[test]
+fn correct_precedence_alias_def_custom() {
+    let actual = nu!(
+        cwd: ".",
+        "def ls [] {echo def}; alias ls = echo alias; which ls | get path | str trim"
+    );
+
+    assert_eq!(actual.out, "Nushell alias: echo alias");
+}
+
+#[test]
+fn multiple_reports_for_alias_def_custom() {
+    let actual = nu!(
+        cwd: ".",
+        "def ls [] {echo def}; alias ls = echo alias; which -a ls | length"
+    );
+
+    let length: i32 = actual.out.parse().unwrap();
+    assert!(length >= 3);
+}
+
+// `get_aliases_with_name` and `get_custom_commands_with_name` don't return the correct count of
+// values
+// I suspect this is due to the ScopeFrame getting discarded at '}' and the command is then
+// executed in the parent scope
+// See: parse_definition, line 2187 for reference.
+#[ignore]
+#[test]
+fn multiple_reports_of_multiple_alias() {
+    let actual = nu!(
+        cwd: ".",
+        "alias xaz = echo alias1; def helper [] {alias xaz = echo alias2; which -a xaz}; helper | length"
+    );
+
+    let length: i32 = actual.out.parse().unwrap();
+    assert_eq!(length, 2);
+}
+
+#[ignore]
+#[test]
+fn multiple_reports_of_multiple_defs() {
+    let actual = nu!(
+        cwd: ".",
+        "def xaz [] {echo def1}; def helper [] { def xaz [] { echo def2 }; which -a xaz }; helper | length"
+    );
+
+    let length: i32 = actual.out.parse().unwrap();
+    assert_eq!(length, 2);
+}
+
+//Fails due to ParserScope::add_definition
+// frame.custom_commands.insert(name.clone(), block.clone());
+// frame.commands.insert(name, whole_stream_command(block));
+#[ignore]
+#[test]
+fn def_only_seen_once() {
+    let actual = nu!(
+        cwd: ".",
+        "def xaz [] {echo def1}; which -a xaz | length"
+    );
+    //length is 2. One custom_command (def) one built in ("wrongly" added)
+    let length: i32 = actual.out.parse().unwrap();
+    assert_eq!(length, 1);
+}