feat(core): Default Response status code to 200

Resolved #6.

Author: offirgolan

packages/@pollyjs/core/src/-private/response.js

@@ -1,18 +1,15 @@
 import stringify from 'json-stable-stringify';
+import assert from '../utils/assert';
 
 const { freeze } = Object;
 
 function formatHeader(name) {
   return (name || '').toLowerCase();
 }
 
-function status(statusCode) {
-  return parseInt(statusCode, 10) || null;
-}
-
 export default class PollyResponse {
   constructor(statusCode, headers, body) {
-    this.statusCode = status(statusCode);
+    this.status(statusCode || 200);
     this.headers = headers || {};
     this.body = body;
   }
@@ -22,7 +19,14 @@ export default class PollyResponse {
   }
 
   status(statusCode) {
-    this.statusCode = status(statusCode);
+    const status = parseInt(statusCode, 10);
+
+    assert(
+      `[Response] Invalid status code: ${status}`,
+      status >= 100 && status < 600
+    );
+
+    this.statusCode = status;
 
     return this;
   }

packages/@pollyjs/core/tests/unit/-private/response-test.js

@@ -9,17 +9,28 @@ describe('Unit | Response', function() {
     expect(new PollyResponse()).to.exist;
   });
 
+  it('should have a default status code of 200', function() {
+    expect(new PollyResponse().statusCode).to.equal(200);
+  });
+
   describe('API', function() {
     beforeEach(function() {
       response = new PollyResponse();
     });
 
     it('.status()', function() {
-      response.status(200);
-      expect(response.statusCode).to.equal(200);
+      [100, '404', 500, '599'].forEach(statusCode => {
+        expect(response.status(statusCode).statusCode).to.equal(
+          Number(statusCode)
+        );
+      });
 
-      response.status('400');
-      expect(response.statusCode).to.equal(400);
+      [null, '', 0, 99, 600, 999].forEach(statusCode => {
+        expect(() => response.status(statusCode)).to.throw(
+          Error,
+          /Invalid status code/
+        );
+      });
     });
 
     it('.getHeader()', function() {