readfilecontext: more tests for coverage + fix AbortError prototype

lib/error.js

@@ -50,6 +50,7 @@ function AbortError() {
   this.name = 'AbortError';
   Error.captureStackTrace(this, AbortError);
 }
+AbortError.prototype = new Error();
 
 /**
  * FSError constructor.

test/lib/readfilecontext.js

@@ -1,12 +1,15 @@
 'use strict';
 
 const helper = require('../helper');
+const fs = require('fs');
+const mock = require('../../lib/index');
 const {
   patchReadFileContext,
   getReadFileContextPrototype
 } = require('../../lib/readfilecontext');
 
 const assert = helper.assert;
+const inVersion = helper.inVersion;
 
 describe('getReadFileContextPrototype', function() {
   it('provides access to the internal ReadFileContext', function() {
@@ -105,3 +108,41 @@ describe('patchReadFileContext', function() {
     });
   });
 });
+
+describe('fs.readFile() with ReadFileContext', function() {
+  // fs.readFile() is already tested elsewhere, here we just make sure we have
+  // coverage of the mocked ReadFileContext implementation.
+
+  beforeEach(function() {
+    mock({
+      'path/to/file.txt': 'file content',
+      1: 'fd content'
+    });
+  });
+  afterEach(mock.restore);
+
+  inVersion('>=15.0.0').it('allows file reads to be aborted', function(done) {
+    const controller = new AbortController();
+    const {signal} = controller;
+
+    fs.readFile('path/to/file.txt', {signal}, function(err) {
+      assert.instanceOf(err, Error);
+      assert.equal(err.name, 'AbortError');
+      assert.equal(err.code, 'ABORT_ERR');
+      done();
+    });
+
+    // By aborting after the call it will be handled by the context rather than readFile()
+    controller.abort();
+  });
+
+  it('allows file reads with a numeric descriptor', function(done) {
+    // This isn't actually supported by mock-fs, but let's make sure the call goes through
+    // It also covers the case of reading an empty file and reading with encoding
+    fs.readFile(1, 'utf-8', function(err, data) {
+      assert.isNull(err);
+      assert.equal(data, '');
+      done();
+    });
+  });
+});