assert: allow number|null as Error.code match

Some errors have numeric codes, or sometimes you want to assert that you
*didn't* get a code on the Error.

src/asserts/src/index.ts

@@ -34,12 +34,12 @@ export type ErrorMessageMatch = {
 }
 
 export type ErrorNameMatch = {
-  name: string | RegExp
+  name: string | RegExp | null | undefined
   [k: string]: any
 }
 
 export type ErrorCodeMatch = {
-  code: string | RegExp
+  code: string | RegExp | number | null | undefined
   [k: string]: any
 }
 

src/asserts/test/index.ts

@@ -474,6 +474,15 @@ t.test('throws, doesNotThrow', t => {
     ),
     { message: 'ok' }
   )
+  t.match(
+    a.throws(
+      () => {
+        throw Object.assign(new Error(''), { code: null, foo: 'bar' })
+      },
+      { code: null, foo: 'bar' }
+    ),
+    { code: null, foo: 'bar' }
+  )
 
   t.end()
 })
@@ -533,6 +542,24 @@ t.test('rejects', async t => {
       throw new Error('ok')
     })
   )
+  t.match(
+    await a.rejects(
+      async () => {
+        throw Object.assign(new Error(''), { code: null, foo: 'bar' })
+      },
+      { code: null, foo: 'bar' }
+    ),
+    { code: null, foo: 'bar' }
+  )
+  t.match(
+    await a.rejects(
+      Promise.reject(
+        Object.assign(new Error(''), { code: null, foo: 'bar' })
+      )
+    ),
+    { code: null, foo: 'bar' },
+    { code: null, foo: 'bar' }
+  )
 })
 
 t.test('resolves', async t => {