Make let a contextual keyword

packages/babel-parser/test/unit/util/identifier.js

@@ -1,18 +1,42 @@
-import { isKeyword } from "../../../src/util/identifier";
+import {
+  isKeyword,
+  keywordRelationalOperator,
+} from "../../../src/util/identifier";
 
 describe("identifier", () => {
   describe("isKeyword", () => {
     it("break is a keyword", () => {
       expect(isKeyword("break")).toBe(true);
     });
-    it("let is a keyword", () => {
-      expect(isKeyword("let")).toBe(true);
+    it("const is a keyword", () => {
+      expect(isKeyword("const")).toBe(true);
     });
     it("super is a keyword", () => {
       expect(isKeyword("super")).toBe(true);
     });
+    it("let is not a keyword", () => {
+      expect(isKeyword("let")).toBe(false);
+    });
     it("abc is not a keyword", () => {
       expect(isKeyword("abc")).toBe(false);
     });
   });
+
+  describe("keywordRelationalOperator", () => {
+    it("in is true", () => {
+      expect(keywordRelationalOperator.test("in")).toBe(true);
+    });
+    it("instanceof is true", () => {
+      expect(keywordRelationalOperator.test("instanceof")).toBe(true);
+    });
+    it("stanceof is false", () => {
+      expect(keywordRelationalOperator.test("stanceof")).toBe(false);
+    });
+    it("instance is false", () => {
+      expect(keywordRelationalOperator.test("instance")).toBe(false);
+    });
+    it("abc is false", () => {
+      expect(keywordRelationalOperator.test("abc")).toBe(false);
+    });
+  });
 });