completely rewrote test suite for top level src files and all builtin files

src/builtin/shift.rs

@@ -35,3 +35,53 @@ pub fn shift(node: Node) -> ShResult<()> {
   state::set_status(0);
   Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+  use crate::state;
+  use crate::testutil::{TestGuard, test_input};
+
+  #[test]
+  fn shift_in_function() {
+    let guard = TestGuard::new();
+    test_input("f() { echo $1; shift 1; echo $1; }").unwrap();
+    test_input("f a b").unwrap();
+    let out = guard.read_output();
+    let lines: Vec<&str> = out.lines().collect();
+    assert_eq!(lines[0], "a");
+    assert_eq!(lines[1], "b");
+  }
+
+  #[test]
+  fn shift_multiple() {
+    let guard = TestGuard::new();
+    test_input("f() { shift 2; echo $1; }").unwrap();
+    test_input("f a b c").unwrap();
+    let out = guard.read_output();
+    assert_eq!(out.trim(), "c");
+  }
+
+  #[test]
+  fn shift_all_params() {
+    let guard = TestGuard::new();
+    test_input("f() { shift 3; echo \"[$1]\"; }").unwrap();
+    test_input("f a b c").unwrap();
+    let out = guard.read_output();
+    assert_eq!(out.trim(), "[]");
+  }
+
+  #[test]
+  fn shift_non_numeric_fails() {
+    let _g = TestGuard::new();
+    let result = test_input("shift abc");
+    assert!(result.is_err());
+  }
+
+  #[test]
+  fn shift_status_zero() {
+    let _g = TestGuard::new();
+    test_input("f() { shift 1; }").unwrap();
+    test_input("f a b").unwrap();
+    assert_eq!(state::get_status(), 0);
+  }
+}