Add wasm tests for lookahead iterator

lib/binding_web/binding.js

@@ -1013,7 +1013,7 @@ class LookaheadIterable {
   }
 
   reset(language, stateId) {
-    if (C._ts_lookahead_iterator_reset(this[0], language, stateId)) {
+    if (C._ts_lookahead_iterator_reset(this[0], language[0], stateId)) {
       this.language = language;
       return true;
     }
@@ -1028,7 +1028,7 @@ class LookaheadIterable {
         if (C._ts_lookahead_iterator_advance(self[0])) {
           return { done: false, value: self.currentType };
         }
-    
+
         return { done: true, value: "" };
       }
     };

lib/binding_web/test/language-test.js

@@ -42,3 +42,41 @@ describe("Language", () => {
     });
   });
 });
+
+describe("Lookahead iterator", () => {
+  let lookahead;
+  let state;
+  before(async () => {
+    let Parser;
+    ({ JavaScript, Parser } = await require("./helper"));
+    const parser = new Parser().setLanguage(JavaScript);
+    const tree = parser.parse("function fn() {}");
+    const cursor = tree.walk();
+    cursor.gotoFirstChild();
+    cursor.gotoFirstChild();
+    state = cursor.currentNode().nextParseState;
+    lookahead = JavaScript.lookaheadIterator(state);
+    assert.exists(lookahead);
+  });
+
+  const expected = ["identifier", "comment", "(", "*", "formal_parameters"];
+  it("should iterate over valid symbols in the state", () => {
+    const symbols = Array.from(lookahead);
+    assert.includeMembers(symbols, expected);
+    assert.lengthOf(symbols, expected.length);
+  });
+
+  it("should reset to the initial state", () => {
+    assert(lookahead.resetState(state));
+    const symbols = Array.from(lookahead);
+    assert.includeMembers(symbols, expected);
+    assert.lengthOf(symbols, expected.length);
+  });
+
+  it("should reset", () => {
+    assert(lookahead.reset(JavaScript, state));
+    const symbols = Array.from(lookahead);
+    assert.includeMembers(symbols, expected);
+    assert.lengthOf(symbols, expected.length);
+  });
+});