Tests for the ErrorContext trait

tests/error.rs

@@ -0,0 +1,33 @@
+use mlua::{Error, ErrorContext, Lua, Result};
+
+#[test]
+fn test_error_context() -> Result<()> {
+    let lua = Lua::new();
+
+    let func = lua.create_function(|_, ()| {
+        Err::<(), _>(Error::RuntimeError("runtime error".into())).context("some context")
+    })?;
+    lua.globals().set("func", func)?;
+
+    let msg = lua
+        .load("local _, err = pcall(func); return tostring(err)")
+        .eval::<String>()?;
+    assert!(msg.contains("some context"));
+    assert!(msg.contains("runtime error"));
+
+    let func2 = lua.create_function(|lua, ()| {
+        lua.globals()
+            .get::<_, String>("nonextant")
+            .with_context(|_| "failed to find global")
+    })?;
+    lua.globals().set("func2", func2)?;
+
+    let msg2 = lua
+        .load("local _, err = pcall(func2); return tostring(err)")
+        .eval::<String>()?;
+    assert!(msg2.contains("failed to find global"));
+    println!("{msg2}");
+    assert!(msg2.contains("error converting Lua nil to String"));
+
+    Ok(())
+}