diff --git a/CHANGELOG.md b/CHANGELOG.md
index 452deb95efe1..257e66b24706 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -107,6 +107,8 @@
 - `[docs]` Add correct default value for `testUrl` config option ([#7277](https://github.com/facebook/jest/pull/7277))
 - `[jest-util]` [**BREAKING**] Remove long-deprecated globals for fake timers ([#7285](https://github.com/facebook/jest/pull/7285))
 - `[docs]` Remove duplicate code in `MockFunctions` ([#7297](https://github.com/facebook/jest/pull/7297))
+- `[jest-worker]` Standardize filenames ([#7316](https://github.com/facebook/jest/pull/7316))
+- `[pretty-format]` Standardize filenames ([#7316](https://github.com/facebook/jest/pull/7316))
 
 ### Performance
 
diff --git a/jest.config.js b/jest.config.js
index 9c16175c878b..9a7e9b0808ce 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -25,7 +25,7 @@ module.exports = {
   projects: ['<rootDir>', '<rootDir>/examples/*/'],
   setupFilesAfterEnv: ['<rootDir>/testSetupFile.js'],
   snapshotSerializers: [
-    '<rootDir>/packages/pretty-format/build/plugins/convert_ansi.js',
+    '<rootDir>/packages/pretty-format/build/plugins/ConvertAnsi.js',
   ],
   testEnvironment: './packages/jest-environment-node',
   testPathIgnorePatterns: [
@@ -35,7 +35,7 @@ module.exports = {
     '\\.snap$',
     '/packages/.*/build',
     '/packages/.*/build-es5',
-    '/packages/.*/src/__tests__/expect_util.js',
+    '/packages/.*/src/__tests__/getPrettyPrint.js',
     '/packages/jest-cli/src/__tests__/test_root',
     '/packages/jest-cli/src/__tests__/__fixtures__/',
     '/packages/jest-cli/src/lib/__tests__/fixtures/',
diff --git a/packages/jest-worker/README.md b/packages/jest-worker/README.md
index 5087287be92a..3c98dfdb2b5e 100644
--- a/packages/jest-worker/README.md
+++ b/packages/jest-worker/README.md
@@ -24,7 +24,7 @@ This example covers the minimal usage:
 import Worker from 'jest-worker';
 
 async function main() {
-  const worker = new Worker(require.resolve('./worker'));
+  const worker = new Worker(require.resolve('./Worker'));
   const result = await worker.hello('Alice'); // "Hello, Alice"
 }
 
@@ -114,7 +114,7 @@ This example covers the standard usage:
 import Worker from 'jest-worker';
 
 async function main() {
-  const myWorker = new Worker(require.resolve('./worker'), {
+  const myWorker = new Worker(require.resolve('./Worker'), {
     exposedMethods: ['foo', 'bar', 'getWorkerId'],
     numWorkers: 4,
   });
@@ -155,7 +155,7 @@ This example covers the usage with a `computeWorkerKey` method:
 import Worker from 'jest-worker';
 
 async function main() {
-  const myWorker = new Worker(require.resolve('./worker'), {
+  const myWorker = new Worker(require.resolve('./Worker'), {
     computeWorkerKey: (method, filename) => filename,
   });
 
diff --git a/packages/jest-worker/src/worker.js b/packages/jest-worker/src/Worker.js
similarity index 100%
rename from packages/jest-worker/src/worker.js
rename to packages/jest-worker/src/Worker.js
diff --git a/packages/jest-worker/src/__tests__/worker.test.js b/packages/jest-worker/src/__tests__/Worker.test.js
similarity index 99%
rename from packages/jest-worker/src/__tests__/worker.test.js
rename to packages/jest-worker/src/__tests__/Worker.test.js
index 4fd91d9e3de6..cad8347df5b9 100644
--- a/packages/jest-worker/src/__tests__/worker.test.js
+++ b/packages/jest-worker/src/__tests__/Worker.test.js
@@ -38,7 +38,7 @@ beforeEach(() => {
     return forkInterface;
   });
 
-  Worker = require('../worker').default;
+  Worker = require('../Worker').default;
 });
 
 afterEach(() => {
diff --git a/packages/jest-worker/src/__tests__/index.test.js b/packages/jest-worker/src/__tests__/index.test.js
index 349a91797b5f..ba49151b6ec2 100644
--- a/packages/jest-worker/src/__tests__/index.test.js
+++ b/packages/jest-worker/src/__tests__/index.test.js
@@ -30,7 +30,7 @@ beforeEach(() => {
   // The worker mock returns a worker with custom methods, plus it stores them
   // in a global list, so that they can be accessed later. This list is reset in
   // every test.
-  jest.mock('../worker', () => {
+  jest.mock('../Worker', () => {
     const fakeClass = jest.fn(() => {
       const fakeWorker = {
         getStderr: () => ({once() {}, pipe() {}}),
@@ -63,7 +63,7 @@ beforeEach(() => {
     virtual: true,
   });
 
-  Worker = require('../worker').default;
+  Worker = require('../Worker').default;
   Farm = require('../index').default;
 });
 
diff --git a/packages/jest-worker/src/index.js b/packages/jest-worker/src/index.js
index 0cb636c2fc6c..be634f2fecbd 100644
--- a/packages/jest-worker/src/index.js
+++ b/packages/jest-worker/src/index.js
@@ -17,7 +17,7 @@ import type {FarmOptions} from './types';
 import type {Readable} from 'stream';
 
 import {CHILD_MESSAGE_CALL, CHILD_MESSAGE_END} from './types';
-import Worker from './worker';
+import Worker from './Worker';
 
 /* istanbul ignore next */
 const emptyMethod = () => {};
diff --git a/packages/jest-worker/src/types.js b/packages/jest-worker/src/types.js
index a8afc71f9f58..5d7108f9fb30 100644
--- a/packages/jest-worker/src/types.js
+++ b/packages/jest-worker/src/types.js
@@ -29,7 +29,7 @@ export type PARENT_MESSAGE_ERROR =
 
 // Option objects.
 
-import type Worker from './worker';
+import type Worker from './Worker';
 
 export type ForkOptions = {
   cwd?: string,
diff --git a/packages/pretty-format/perf/test.js b/packages/pretty-format/perf/test.js
index 9bc97b44099f..e8ac99df480c 100644
--- a/packages/pretty-format/perf/test.js
+++ b/packages/pretty-format/perf/test.js
@@ -12,7 +12,7 @@ const React = require('react');
 const ReactTestRenderer = require('react-test-renderer');
 const leftPad = require('left-pad');
 const prettyFormat = require('../build');
-const ReactTestComponent = require('../build/plugins/react_test_component');
+const ReactTestComponent = require('../build/plugins/ReactTestComponent');
 const worldGeoJson = require('./world.geo.json');
 
 const NANOSECONDS = 1000000000;
diff --git a/packages/pretty-format/src/__tests__/asymmetric_matcher.test.js b/packages/pretty-format/src/__tests__/AsymmetricMatcher.test.js
similarity index 100%
rename from packages/pretty-format/src/__tests__/asymmetric_matcher.test.js
rename to packages/pretty-format/src/__tests__/AsymmetricMatcher.test.js
diff --git a/packages/pretty-format/src/__tests__/convert_ansi.test.js b/packages/pretty-format/src/__tests__/ConvertAnsi.test.js
similarity index 100%
rename from packages/pretty-format/src/__tests__/convert_ansi.test.js
rename to packages/pretty-format/src/__tests__/ConvertAnsi.test.js
diff --git a/packages/pretty-format/src/__tests__/dom_collection.test.js b/packages/pretty-format/src/__tests__/DOMCollection.test.js
similarity index 98%
rename from packages/pretty-format/src/__tests__/dom_collection.test.js
rename to packages/pretty-format/src/__tests__/DOMCollection.test.js
index cf0d498f8b18..204068c2561c 100644
--- a/packages/pretty-format/src/__tests__/dom_collection.test.js
+++ b/packages/pretty-format/src/__tests__/DOMCollection.test.js
@@ -13,7 +13,7 @@
 
 const prettyFormat = require('../');
 const {DOMCollection, DOMElement} = prettyFormat.plugins;
-const toPrettyPrintTo = require('./expect_util').getPrettyPrint([
+const toPrettyPrintTo = require('./getPrettyPrint').default([
   DOMCollection,
   DOMElement,
 ]);
diff --git a/packages/pretty-format/src/__tests__/dom_element.test.js b/packages/pretty-format/src/__tests__/DOMElement.test.js
similarity index 99%
rename from packages/pretty-format/src/__tests__/dom_element.test.js
rename to packages/pretty-format/src/__tests__/DOMElement.test.js
index 9b06b105766c..e211b33665d9 100644
--- a/packages/pretty-format/src/__tests__/dom_element.test.js
+++ b/packages/pretty-format/src/__tests__/DOMElement.test.js
@@ -13,7 +13,7 @@
 
 const prettyFormat = require('../');
 const {DOMElement} = prettyFormat.plugins;
-const toPrettyPrintTo = require('./expect_util').getPrettyPrint([DOMElement]);
+const toPrettyPrintTo = require('./getPrettyPrint').default([DOMElement]);
 
 const expect: any = global.expect;
 expect.extend({toPrettyPrintTo});
diff --git a/packages/pretty-format/src/__tests__/immutable.test.js b/packages/pretty-format/src/__tests__/Immutable.test.js
similarity index 99%
rename from packages/pretty-format/src/__tests__/immutable.test.js
rename to packages/pretty-format/src/__tests__/Immutable.test.js
index b402605cf85c..4e0e40cf91e7 100644
--- a/packages/pretty-format/src/__tests__/immutable.test.js
+++ b/packages/pretty-format/src/__tests__/Immutable.test.js
@@ -11,7 +11,7 @@
 
 import React from 'react';
 import Immutable from 'immutable';
-import {getPrettyPrint} from './expect_util';
+import getPrettyPrint from './getPrettyPrint';
 
 const {plugins: prettyPlugins} = require('..');
 const {Immutable: ImmutablePlugin, ReactElement} = prettyPlugins;
diff --git a/packages/pretty-format/src/__tests__/expect_util.js b/packages/pretty-format/src/__tests__/getPrettyPrint.js
similarity index 95%
rename from packages/pretty-format/src/__tests__/expect_util.js
rename to packages/pretty-format/src/__tests__/getPrettyPrint.js
index 1fb9a1dc0d8b..5ee5ee04929b 100644
--- a/packages/pretty-format/src/__tests__/expect_util.js
+++ b/packages/pretty-format/src/__tests__/getPrettyPrint.js
@@ -14,7 +14,7 @@ import type {OptionsReceived, Plugins} from 'types/PrettyFormat';
 const diff = require('jest-diff');
 const prettyFormat = require('../');
 
-export const getPrettyPrint = (plugins: Plugins) =>
+const getPrettyPrint = (plugins: Plugins) =>
   function(received: any, expected: any, options?: OptionsReceived) {
     const prettyFormatted = prettyFormat(
       received,
@@ -52,3 +52,5 @@ export const getPrettyPrint = (plugins: Plugins) =>
 
     return {actual: prettyFormatted, message, pass};
   };
+
+export default getPrettyPrint;
diff --git a/packages/pretty-format/src/__tests__/pretty_format.test.js b/packages/pretty-format/src/__tests__/prettyFormat.test.js
similarity index 100%
rename from packages/pretty-format/src/__tests__/pretty_format.test.js
rename to packages/pretty-format/src/__tests__/prettyFormat.test.js
diff --git a/packages/pretty-format/src/index.js b/packages/pretty-format/src/index.js
index 3c193f1a17d3..618a6fc62971 100644
--- a/packages/pretty-format/src/index.js
+++ b/packages/pretty-format/src/index.js
@@ -28,13 +28,13 @@ import {
   printObjectProperties,
 } from './collections';
 
-import AsymmetricMatcher from './plugins/asymmetric_matcher';
-import ConvertAnsi from './plugins/convert_ansi';
-import DOMCollection from './plugins/dom_collection';
-import DOMElement from './plugins/dom_element';
-import Immutable from './plugins/immutable';
-import ReactElement from './plugins/react_element';
-import ReactTestComponent from './plugins/react_test_component';
+import AsymmetricMatcher from './plugins/AsymmetricMatcher';
+import ConvertAnsi from './plugins/ConvertAnsi';
+import DOMCollection from './plugins/DOMCollection';
+import DOMElement from './plugins/DOMElement';
+import Immutable from './plugins/Immutable';
+import ReactElement from './plugins/ReactElement';
+import ReactTestComponent from './plugins/ReactTestComponent';
 
 const toString = Object.prototype.toString;
 const toISOString = Date.prototype.toISOString;
diff --git a/packages/pretty-format/src/plugins/asymmetric_matcher.js b/packages/pretty-format/src/plugins/AsymmetricMatcher.js
similarity index 100%
rename from packages/pretty-format/src/plugins/asymmetric_matcher.js
rename to packages/pretty-format/src/plugins/AsymmetricMatcher.js
diff --git a/packages/pretty-format/src/plugins/convert_ansi.js b/packages/pretty-format/src/plugins/ConvertAnsi.js
similarity index 100%
rename from packages/pretty-format/src/plugins/convert_ansi.js
rename to packages/pretty-format/src/plugins/ConvertAnsi.js
diff --git a/packages/pretty-format/src/plugins/dom_collection.js b/packages/pretty-format/src/plugins/DOMCollection.js
similarity index 100%
rename from packages/pretty-format/src/plugins/dom_collection.js
rename to packages/pretty-format/src/plugins/DOMCollection.js
diff --git a/packages/pretty-format/src/plugins/dom_element.js b/packages/pretty-format/src/plugins/DOMElement.js
similarity index 100%
rename from packages/pretty-format/src/plugins/dom_element.js
rename to packages/pretty-format/src/plugins/DOMElement.js
diff --git a/packages/pretty-format/src/plugins/immutable.js b/packages/pretty-format/src/plugins/Immutable.js
similarity index 100%
rename from packages/pretty-format/src/plugins/immutable.js
rename to packages/pretty-format/src/plugins/Immutable.js
diff --git a/packages/pretty-format/src/plugins/react_element.js b/packages/pretty-format/src/plugins/ReactElement.js
similarity index 100%
rename from packages/pretty-format/src/plugins/react_element.js
rename to packages/pretty-format/src/plugins/ReactElement.js
diff --git a/packages/pretty-format/src/plugins/react_test_component.js b/packages/pretty-format/src/plugins/ReactTestComponent.js
similarity index 100%
rename from packages/pretty-format/src/plugins/react_test_component.js
rename to packages/pretty-format/src/plugins/ReactTestComponent.js
diff --git a/packages/pretty-format/src/plugins/lib/escape_html.js b/packages/pretty-format/src/plugins/lib/escapeHTML.js
similarity index 100%
rename from packages/pretty-format/src/plugins/lib/escape_html.js
rename to packages/pretty-format/src/plugins/lib/escapeHTML.js
diff --git a/packages/pretty-format/src/plugins/lib/markup.js b/packages/pretty-format/src/plugins/lib/markup.js
index eb45835588a0..70ebceebc806 100644
--- a/packages/pretty-format/src/plugins/lib/markup.js
+++ b/packages/pretty-format/src/plugins/lib/markup.js
@@ -9,7 +9,7 @@
 
 import type {Config, Printer, Refs} from 'types/PrettyFormat';
 
-import escapeHTML from './escape_html';
+import escapeHTML from './escapeHTML';
 
 // Return empty string if keys is empty.
 export const printProps = (