From 180296dc6f489828a86bbd9b9b87010584cbd37b Mon Sep 17 00:00:00 2001
From: Brian Cully <bjc@spork.org>
Date: Mon, 25 Aug 2025 15:09:04 -0400
Subject: some underflow tests

---
 src/forth/vm.rs | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

(limited to 'src')

diff --git a/src/forth/vm.rs b/src/forth/vm.rs
index e5973dd..2305393 100644
--- a/src/forth/vm.rs
+++ b/src/forth/vm.rs
@@ -112,7 +112,7 @@ pub struct VM {
     pub ip: InstructionPointer,
 }
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq, Eq)]
 pub enum RuntimeError {
     StackUnderflow,
 }
@@ -595,6 +595,16 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn opcode_dup_underflow() -> Result<(), RuntimeError> {
+        let wordlist = wl_for(vec![
+            vec![OpCode::Dup],
+        ]);
+        let mut vm = VM::new(wordlist);
+        assert!(vm.run().is_err_and(|e| e == RuntimeError::StackUnderflow));
+        Ok(())
+    }
+
     #[test]
     fn opcode_swap() -> Result<(), RuntimeError> {
         let wordlist = wl_for(vec![
@@ -606,6 +616,16 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn opcode_swap_underflow() -> Result<(), RuntimeError> {
+        let wordlist = wl_for(vec![
+            vec![OpCode::Num(1), OpCode::Swap],
+        ]);
+        let mut vm = VM::new(wordlist);
+        assert!(vm.run().is_err_and(|e| e == RuntimeError::StackUnderflow));
+        Ok(())
+    }
+
     #[test]
     fn opcode_rot() -> Result<(), RuntimeError> {
         let wordlist = wl_for(vec![
@@ -617,6 +637,16 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn opcode_rot_underflow() -> Result<(), RuntimeError> {
+        let wordlist = wl_for(vec![
+            vec![OpCode::Num(1), OpCode::Num(2), OpCode::Rot],
+        ]);
+        let mut vm = VM::new(wordlist);
+        assert!(vm.run().is_err_and(|e| e == RuntimeError::StackUnderflow));
+        Ok(())
+    }
+
     #[test]
     fn tif_no_ret() -> Result<(), RuntimeError> {
         let wordlist = wl_for(vec![
-- 
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