Add initial nu-test-support port (#913)

* Add initial nu-test-support port

* finish changing binary name

* Oops, these aren't Windows-safe tests

crates/nu-test-support/src/commands.rs

@@ -0,0 +1,53 @@
+// use nu_protocol::{
+//     ast::{Expr, Expression},
+//     Span, Spanned, Type,
+// };
+
+// pub struct ExternalBuilder {
+//     name: String,
+//     args: Vec<String>,
+// }
+
+// impl ExternalBuilder {
+//     pub fn for_name(name: &str) -> ExternalBuilder {
+//         ExternalBuilder {
+//             name: name.to_string(),
+//             args: vec![],
+//         }
+//     }
+
+//     pub fn arg(&mut self, value: &str) -> &mut Self {
+//         self.args.push(value.to_string());
+//         self
+//     }
+
+// pub fn build(&mut self) -> ExternalCommand {
+//     let mut path = crate::fs::binaries();
+//     path.push(&self.name);
+
+//     let name = Spanned {
+//         item: path.to_string_lossy().to_string(),
+//         span: Span::new(0, 0),
+//     };
+
+//     let args = self
+//         .args
+//         .iter()
+//         .map(|arg| Expression {
+//             expr: Expr::String(arg.to_string()),
+//             span: Span::new(0, 0),
+//             ty: Type::Unknown,
+//             custom_completion: None,
+//         })
+//         .collect::<Vec<_>>();
+
+//     ExternalCommand {
+//         name: name.to_string(),
+//         name_tag: Tag::unknown(),
+//         args: ExternalArgs {
+//             list: args,
+//             span: name.span,
+//         },
+//     }
+// }
+// }