add more tests for new $in behaviour

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

@@ -439,3 +439,37 @@ fn no_duplicate_redirection() {
         );
     });
 }
+
+#[rstest::rstest]
+#[case("let", "out>")]
+#[case("let", "err>")]
+#[case("let", "out+err>")]
+#[case("mut", "out>")]
+#[case("mut", "err>")]
+#[case("mut", "out+err>")]
+fn file_redirection_in_let_and_mut(#[case] keyword: &str, #[case] redir: &str) {
+    Playground::setup("file redirection in let and mut", |dirs, _| {
+        let actual = nu!(
+            cwd: dirs.test(),
+            format!("$env.BAZ = 'foo'; {keyword} v = nu --testbin echo_env_mixed out-err BAZ BAZ {redir} result.txt")
+        );
+        assert!(actual.status.success());
+        assert!(file_contents(dirs.test().join("result.txt")).contains("foo"));
+    })
+}
+
+#[rstest::rstest]
+#[case("let", "err>|", 3)]
+#[case("let", "out+err>|", 6)]
+#[case("mut", "err>|", 3)]
+#[case("mut", "out+err>|", 6)]
+fn pipe_redirection_in_let_and_mut(
+    #[case] keyword: &str,
+    #[case] redir: &str,
+    #[case] length: usize,
+) {
+    let actual = nu!(
+        format!("$env.BAZ = 'foo'; {keyword} v = nu --testbin echo_env_mixed out-err BAZ BAZ {redir} str length; $v")
+    );
+    assert_eq!(actual.out.len(), length);
+}

tests/repl/test_engine.rs

@@ -52,6 +52,21 @@ fn in_and_if_else() -> TestResult {
     )
 }
 
+#[test]
+fn in_with_closure() -> TestResult {
+    // Can use $in twice
+    run_test(r#"3 | do { let x = $in; let y = $in; $x + $y }"#, "6")
+}
+
+#[test]
+fn in_with_custom_command() -> TestResult {
+    // Can use $in twice
+    run_test(
+        r#"def foo [] { let x = $in; let y = $in; $x + $y }; 3 | foo"#,
+        "6",
+    )
+}
+
 #[test]
 fn help_works_with_missing_requirements() -> TestResult {
     run_test(r#"each --help | lines | length"#, "72")

tests/repl/test_type_check.rs

@@ -129,3 +129,16 @@ fn transpose_into_load_env() -> TestResult {
         "10",
     )
 }
+
+#[test]
+fn in_variable_expression_correct_output_type() -> TestResult {
+    run_test(r#"def foo []: nothing -> string { 'foo' | $"($in)" }"#, "")
+}
+
+#[test]
+fn in_variable_expression_wrong_output_type() -> TestResult {
+    fail_test(
+        r#"def foo []: nothing -> int { 'foo' | $"($in)" }"#,
+        "expected int",
+    )
+}