A set of fixes for stderr redirect (#7219)

# Description

This is a set of fixes to `err>` to make it work a bit more predictably.

I've also revised the tests, which accidentally tested the wrong thing
for redirection, but should be more correct now.

# User-Facing Changes

_(List of all changes that impact the user experience here. This helps
us keep track of breaking changes.)_

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

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

@@ -9,6 +9,8 @@ fn capture_errors_works() {
         "#
     ));
 
+    eprintln!("actual.err: {:?}", actual.err);
+
     assert!(actual.err.contains("column_not_found"));
 }
 
@@ -65,7 +67,7 @@ fn ignore_shell_errors_works_for_external_with_semicolon() {
     let actual = nu!(
         cwd: ".", pipeline(
         r#"
-        do -s { fail }; `text`
+        do -s { open asdfasdf.txt }; "text"
         "#
     ));
 

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

@@ -323,7 +323,7 @@ fn parse_string_as_script() {
             "#
         ));
 
-        println!("the out put is {}", actual.err);
+        println!("the output is {}", actual.err);
         assert!(actual.err.contains("Failed to parse content"));
     })
 }

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

@@ -7,10 +7,10 @@ fn redirect_err() {
     Playground::setup("redirect_err_test", |dirs, _sandbox| {
         let output = nu!(
             cwd: dirs.test(),
-            "cat asdfasdfasdf.txt err> a; cat a"
+            "cat asdfasdfasdf.txt err> a.txt; cat a.txt"
         );
 
-        assert!(output.err.contains("asdfasdfasdf.txt"));
+        assert!(output.out.contains("asdfasdfasdf.txt"));
     })
 }
 
@@ -20,10 +20,10 @@ fn redirect_err() {
     Playground::setup("redirect_err_test", |dirs, _sandbox| {
         let output = nu!(
             cwd: dirs.test(),
-            "type asdfasdfasdf.txt err> a; type a"
+            "dir missingapplication err> a; (open a | size).bytes >= 16"
         );
 
-        assert!(output.err.contains("asdfasdfasdf.txt"));
+        assert!(output.out.contains("true"));
     })
 }
 
@@ -36,7 +36,7 @@ fn redirect_outerr() {
             "cat asdfasdfasdf.txt out+err> a; cat a"
         );
 
-        assert!(output.err.contains("asdfasdfasdf.txt"));
+        assert!(output.out.contains("asdfasdfasdf.txt"));
     })
 }
 
@@ -46,10 +46,10 @@ fn redirect_outerr() {
     Playground::setup("redirect_outerr_test", |dirs, _sandbox| {
         let output = nu!(
             cwd: dirs.test(),
-            "type asdfasdfasdf.txt out+err> a; type a"
+            "dir missingapplication out+err> a; (open a | size).bytes >= 16"
         );
 
-        assert!(output.err.contains("asdfasdfasdf.txt"));
+        assert!(output.out.contains("true"));
     })
 }