This commit is the continuing phase of extracting functionality to subcrates. We extract test helpers and begin to change Nu shell's test organization along with it.

tests/commands/mod.rs

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+mod append;
+mod cd;
+mod compact;
+mod cp;
+mod default;
+mod edit;
+mod enter;
+mod first;
+mod format;
+mod get;
+mod group_by;
+mod histogram;
+mod insert;
+mod last;
+mod lines;
+mod ls;
+mod mkdir;
+mod mv;
+mod open;
+mod parse;
+mod prepend;
+mod range;
+mod reverse;
+mod rm;
+mod save;
+mod sort_by;
+mod split_by;
+mod split_column;
+mod where_;
+mod wrap;