feat(api): Mockup how to use and test a Rust function from Lua

core/sile.lua

@@ -16,6 +16,10 @@ SILE = {}
 --- Fields
 -- @section fields
 
+--- Functions implemented in Rust, to be moved to approprate places in the API
+-- @table SILE.rusile
+SILE._rusile = require("rusile")
+
 --- Machine friendly short-form version.
 -- Semver, prefixed with "v", possible postfixed with ".r" followed by VCS version information.
 -- @string version

rusile/src/lib.rs

@@ -7,5 +7,11 @@ use mlua::prelude::*;
 #[mlua::lua_module]
 fn rusile(lua: &Lua) -> LuaResult<LuaTable> {
     let exports = lua.create_table().unwrap();
+    let foo: LuaFunction = lua.create_function(foo).unwrap();
+    exports.set("foo", foo)?;
     Ok(exports)
 }
+
+fn foo(lua: &Lua, (): ()) -> LuaResult<LuaString> {
+    lua.create_string("Hello from rusile")
+}

spec/rusile_spec.lua

@@ -0,0 +1,16 @@
+SILE = require("core.sile")
+
+describe("rusile", function ()
+
+   it("should exist", function ()
+      assert.is.truthy(SILE._rusile)
+   end)
+
+   describe("foo ", function ()
+      it("should return a test string", function ()
+         local str = "Hello from rusile"
+         assert.is.equal(str, SILE._rusile.foo())
+      end)
+   end)
+
+end)