diff --git a/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
new file mode 100644
index 00000000000..5961532b462
--- /dev/null
+++ b/Libraries/LogBox/Data/__tests__/LogBoxLog-test.js
@@ -0,0 +1,150 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+react_native
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+import type {StackFrame} from '../../../Core/NativeExceptionsManager';
+
+jest.mock('../LogBoxSymbolication', () => {
+  return {__esModule: true, symbolicate: jest.fn(), deleteStack: jest.fn()};
+});
+
+function getLogBoxLog() {
+  return new (require('../LogBoxLog')).default(
+    {content: '...', substitutions: []},
+    createStack(['A', 'B', 'C']),
+    'Message category...',
+    [{component: 'LogBoxLog', location: 'LogBoxLog.js:1'}],
+    true,
+  );
+}
+
+function getLogBoxSymbolication(): {|
+  symbolicate: JestMockFn<
+    $ReadOnlyArray<Array<StackFrame>>,
+    Promise<Array<StackFrame>>,
+  >,
+|} {
+  return (require('../LogBoxSymbolication'): any);
+}
+
+const createStack = methodNames =>
+  methodNames.map(methodName => ({
+    column: null,
+    file: 'file://path/to/file.js',
+    lineNumber: 1,
+    methodName,
+  }));
+
+describe('LogBoxLog', () => {
+  beforeEach(() => {
+    jest.resetModules();
+
+    getLogBoxSymbolication().symbolicate.mockImplementation(async stack =>
+      createStack(stack.map(frame => `S(${frame.methodName})`)),
+    );
+  });
+
+  it('creates a LogBoxLog object', () => {
+    const log = getLogBoxLog();
+
+    expect(log.message).toEqual({content: '...', substitutions: []});
+    expect(log.stack).toEqual(createStack(['A', 'B', 'C']));
+    expect(log.category).toEqual('Message category...');
+    expect(log.componentStack).toEqual([
+      {component: 'LogBoxLog', location: 'LogBoxLog.js:1'},
+    ]);
+    expect(log.ignored).toEqual(true);
+  });
+
+  it('increments LogBoxLog count', () => {
+    const log = getLogBoxLog();
+
+    expect(log.count).toEqual(1);
+
+    log.incrementCount();
+
+    expect(log.count).toEqual(2);
+  });
+
+  it('starts without a symbolicated stack', () => {
+    const log = getLogBoxLog();
+
+    expect(log.symbolicated).toEqual({
+      error: null,
+      stack: null,
+      status: 'NONE',
+    });
+  });
+
+  it('updates when symbolication is in progress', () => {
+    const log = getLogBoxLog();
+
+    const callback = jest.fn();
+    log.symbolicate(callback);
+
+    expect(callback.mock.calls.length).toBe(1);
+    expect(log.symbolicated).toEqual({
+      error: null,
+      stack: null,
+      status: 'PENDING',
+    });
+  });
+
+  it('updates when symbolication finishes', () => {
+    const log = getLogBoxLog();
+
+    const callback = jest.fn();
+    log.symbolicate(callback);
+
+    jest.runAllTicks();
+
+    expect(callback.mock.calls.length).toBe(2);
+    expect(log.symbolicated).toEqual({
+      error: null,
+      stack: createStack(['S(A)', 'S(B)', 'S(C)']),
+      status: 'COMPLETE',
+    });
+  });
+
+  it('updates when symbolication fails', () => {
+    const error = new Error('...');
+    getLogBoxSymbolication().symbolicate.mockImplementation(async stack => {
+      throw error;
+    });
+
+    const log = getLogBoxLog();
+
+    const callback = jest.fn();
+    log.symbolicate(callback);
+
+    jest.runAllTicks();
+
+    expect(callback.mock.calls.length).toBe(2);
+    expect(log.symbolicated).toEqual({
+      error,
+      stack: null,
+      status: 'FAILED',
+    });
+  });
+
+  it('does not update aborted requests', () => {
+    const log = getLogBoxLog();
+
+    const callback = jest.fn();
+    const request = log.symbolicate(callback);
+    request.abort();
+
+    jest.runAllTicks();
+
+    expect(callback.mock.calls.length).toBe(1);
+  });
+});
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxLogData-test.js b/Libraries/LogBox/Data/__tests__/LogBoxLogData-test.js
new file mode 100644
index 00000000000..a00b50d2b3f
--- /dev/null
+++ b/Libraries/LogBox/Data/__tests__/LogBoxLogData-test.js
@@ -0,0 +1,308 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+react_native
+ * @format
+ * @flow strict-local
+ */
+
+'use strict';
+jest.mock('../../../Core/Devtools/parseErrorStack', () => {
+  return {__esModule: true, default: jest.fn(() => [])};
+});
+
+const LogBoxLogData = require('../LogBoxLogData');
+
+const registry = () => {
+  const observer = jest.fn();
+  LogBoxLogData.observe(observer).unsubscribe();
+  return observer.mock.calls[0][0];
+};
+
+const filteredRegistry = () => {
+  const observer = jest.fn();
+  LogBoxLogData.observe(observer).unsubscribe();
+  return observer.mock.calls[0][0].filter(log => !log.ignored);
+};
+
+const observe = () => {
+  const observer = jest.fn();
+  return {
+    observer,
+    subscription: LogBoxLogData.observe(observer),
+  };
+};
+
+describe('LogBoxLogData', () => {
+  beforeEach(() => {
+    jest.resetModules();
+  });
+
+  it('adds and dismisses logs', () => {
+    LogBoxLogData.add({args: ['A']});
+
+    expect(registry().length).toBe(1);
+    expect(registry()[0]).toBeDefined();
+
+    LogBoxLogData.dismiss(registry()[0]);
+    expect(registry().length).toBe(0);
+    expect(registry()[0]).toBeUndefined();
+  });
+
+  it('clears all logs', () => {
+    LogBoxLogData.add({args: ['A']});
+    LogBoxLogData.add({args: ['B']});
+    LogBoxLogData.add({args: ['C']});
+
+    expect(registry().length).toBe(3);
+
+    LogBoxLogData.clear();
+    expect(registry().length).toBe(0);
+  });
+
+  it('keeps logs in chronological order', () => {
+    LogBoxLogData.add({args: ['A']});
+    LogBoxLogData.add({args: ['B']});
+    LogBoxLogData.add({args: ['C']});
+
+    let logs = registry();
+    expect(logs.length).toBe(3);
+    expect(logs[0].category).toEqual('A');
+    expect(logs[1].category).toEqual('B');
+    expect(logs[2].category).toEqual('C');
+
+    LogBoxLogData.add({args: ['A']});
+
+    // Expect `A` to be added to the end of the registry.
+    logs = registry();
+    expect(logs.length).toBe(4);
+    expect(logs[0].category).toEqual('A');
+    expect(logs[1].category).toEqual('B');
+    expect(logs[2].category).toEqual('C');
+    expect(logs[3].category).toEqual('A');
+  });
+
+  it('increments the count of previous log with matching category', () => {
+    LogBoxLogData.add({args: ['A']});
+    LogBoxLogData.add({args: ['B']});
+
+    let logs = registry();
+    expect(logs.length).toBe(2);
+    expect(logs[0].category).toEqual('A');
+    expect(logs[0].count).toBe(1);
+    expect(logs[1].category).toEqual('B');
+    expect(logs[1].count).toBe(1);
+
+    LogBoxLogData.add({args: ['B']});
+
+    // Expect `B` to be rolled into the last log.
+    logs = registry();
+    expect(logs.length).toBe(2);
+    expect(logs[0].category).toEqual('A');
+    expect(logs[0].count).toBe(1);
+    expect(logs[1].category).toEqual('B');
+    expect(logs[1].count).toBe(2);
+  });
+
+  it('ignores logs matching patterns', () => {
+    LogBoxLogData.add({args: ['A!']});
+    LogBoxLogData.add({args: ['B?']});
+    LogBoxLogData.add({args: ['C!']});
+    expect(filteredRegistry().length).toBe(3);
+
+    LogBoxLogData.addIgnorePatterns(['!']);
+    expect(filteredRegistry().length).toBe(1);
+
+    LogBoxLogData.addIgnorePatterns(['?']);
+    expect(filteredRegistry().length).toBe(0);
+  });
+
+  it('ignores logs matching regexs or pattern', () => {
+    LogBoxLogData.add({args: ['There are 4 dogs']});
+    LogBoxLogData.add({args: ['There are 3 cats']});
+    LogBoxLogData.add({args: ['There are H cats']});
+    expect(filteredRegistry().length).toBe(3);
+
+    LogBoxLogData.addIgnorePatterns(['dogs']);
+    expect(filteredRegistry().length).toBe(2);
+
+    LogBoxLogData.addIgnorePatterns([/There are \d+ cats/]);
+    expect(filteredRegistry().length).toBe(1);
+
+    LogBoxLogData.addIgnorePatterns(['cats']);
+    expect(filteredRegistry().length).toBe(0);
+  });
+
+  it('ignores all logs when disabled', () => {
+    LogBoxLogData.add({args: ['A!']});
+    LogBoxLogData.add({args: ['B?']});
+    LogBoxLogData.add({args: ['C!']});
+    expect(registry().length).toBe(3);
+
+    LogBoxLogData.setDisabled(true);
+    expect(registry().length).toBe(0);
+
+    LogBoxLogData.setDisabled(false);
+    expect(registry().length).toBe(3);
+  });
+
+  it('groups consecutive logs by format string categories', () => {
+    LogBoxLogData.add({args: ['%s', 'A']});
+    expect(registry().length).toBe(1);
+    expect(registry()[0].count).toBe(1);
+
+    LogBoxLogData.add({args: ['%s', 'B']});
+    expect(registry().length).toBe(1);
+    expect(registry()[0].count).toBe(2);
+
+    LogBoxLogData.add({args: ['A']});
+    expect(registry().length).toBe(2);
+    expect(registry()[1].count).toBe(1);
+
+    LogBoxLogData.add({args: ['B']});
+    expect(registry().length).toBe(3);
+    expect(registry()[2].count).toBe(1);
+  });
+
+  it('groups warnings with consideration for arguments', () => {
+    LogBoxLogData.add({args: ['A', 'B']});
+    expect(registry().length).toBe(1);
+    expect(registry()[0].count).toBe(1);
+
+    LogBoxLogData.add({args: ['A', 'B']});
+    expect(registry().length).toBe(1);
+    expect(registry()[0].count).toBe(2);
+
+    LogBoxLogData.add({args: ['A', 'C']});
+    expect(registry().length).toBe(2);
+    expect(registry()[1].count).toBe(1);
+
+    LogBoxLogData.add({args: ['%s', 'A', 'A']});
+    expect(registry().length).toBe(3);
+    expect(registry()[2].count).toBe(1);
+
+    LogBoxLogData.add({args: ['%s', 'B', 'A']});
+    expect(registry().length).toBe(3);
+    expect(registry()[2].count).toBe(2);
+
+    LogBoxLogData.add({args: ['%s', 'B', 'B']});
+    expect(registry().length).toBe(4);
+    expect(registry()[3].count).toBe(1);
+  });
+
+  it('ignores logs starting with "(ADVICE)"', () => {
+    LogBoxLogData.add({args: ['(ADVICE) ...']});
+    expect(registry().length).toBe(0);
+  });
+
+  it('does not ignore logs formatted to start with "(ADVICE)"', () => {
+    LogBoxLogData.add({args: ['%s ...', '(ADVICE)']});
+    expect(registry().length).toBe(1);
+  });
+
+  it('immediately updates new observers', () => {
+    const {observer} = observe();
+
+    expect(observer.mock.calls.length).toBe(1);
+    expect(observer.mock.calls[0][0]).toEqual(registry());
+  });
+
+  it('sends batched updates asynchronously', () => {
+    const {observer} = observe();
+    expect(observer.mock.calls.length).toBe(1);
+
+    LogBoxLogData.add({args: ['A']});
+    LogBoxLogData.add({args: ['B']});
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+  });
+
+  it('stops sending updates to unsubscribed observers', () => {
+    const {observer, subscription} = observe();
+    subscription.unsubscribe();
+
+    expect(observer.mock.calls.length).toBe(1);
+    expect(observer.mock.calls[0][0]).toEqual(registry());
+  });
+
+  it('updates observers when a log is added or dismissed', () => {
+    const {observer} = observe();
+    expect(observer.mock.calls.length).toBe(1);
+
+    LogBoxLogData.add({args: ['A']});
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+
+    const lastLog = observer.mock.calls[1][0][0];
+    LogBoxLogData.dismiss(lastLog);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+
+    // Does nothing when category does not exist.
+    LogBoxLogData.dismiss(lastLog);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+  });
+
+  it('updates observers when cleared', () => {
+    const {observer} = observe();
+    expect(observer.mock.calls.length).toBe(1);
+
+    LogBoxLogData.add({args: ['A']});
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+
+    LogBoxLogData.clear();
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+
+    // Does nothing when already empty.
+    LogBoxLogData.clear();
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+  });
+
+  it('updates observers when an ignore pattern is added', () => {
+    const {observer} = observe();
+    expect(observer.mock.calls.length).toBe(1);
+
+    LogBoxLogData.addIgnorePatterns(['?']);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+
+    LogBoxLogData.addIgnorePatterns(['!']);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+
+    // Does nothing for an existing ignore pattern.
+    LogBoxLogData.addIgnorePatterns(['!']);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+  });
+
+  it('updates observers when disabled or enabled', () => {
+    const {observer} = observe();
+    expect(observer.mock.calls.length).toBe(1);
+
+    LogBoxLogData.setDisabled(true);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+
+    // Does nothing when already disabled.
+    LogBoxLogData.setDisabled(true);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(2);
+
+    LogBoxLogData.setDisabled(false);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+
+    // Does nothing when already enabled.
+    LogBoxLogData.setDisabled(false);
+    jest.runAllImmediates();
+    expect(observer.mock.calls.length).toBe(3);
+  });
+});
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxLogParser-test.js b/Libraries/LogBox/Data/__tests__/LogBoxLogParser-test.js
new file mode 100644
index 00000000000..9b21122bd0c
--- /dev/null
+++ b/Libraries/LogBox/Data/__tests__/LogBoxLogParser-test.js
@@ -0,0 +1,160 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+react_native
+ * @format
+ * @flow strict-local
+ */
+
+'use strict';
+
+jest.mock('../../../Core/Devtools/parseErrorStack', () => {
+  return {__esModule: true, default: jest.fn(() => [])};
+});
+
+const LogBoxLogParser = require('../LogBoxLogParser').default;
+
+describe('LogBoxLogParser', () => {
+  it('parses strings', () => {
+    expect(LogBoxLogParser({args: ['A']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: 'A',
+      message: {
+        content: 'A',
+        substitutions: [],
+      },
+    });
+  });
+
+  it('parses strings with arguments', () => {
+    expect(LogBoxLogParser({args: ['A', 'B', 'C']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: 'A B C',
+      message: {
+        content: 'A B C',
+        substitutions: [],
+      },
+    });
+  });
+
+  it('parses formatted strings', () => {
+    expect(LogBoxLogParser({args: ['%s', 'A']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: '\ufeff%s',
+      message: {
+        content: 'A',
+        substitutions: [
+          {
+            length: 1,
+            offset: 0,
+          },
+        ],
+      },
+    });
+  });
+
+  it('parses formatted strings with insufficient arguments', () => {
+    expect(LogBoxLogParser({args: ['%s %s', 'A']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: '\ufeff%s %s',
+      message: {
+        content: 'A %s',
+        substitutions: [
+          {
+            length: 1,
+            offset: 0,
+          },
+          {
+            length: 2,
+            offset: 2,
+          },
+        ],
+      },
+    });
+  });
+
+  it('parses formatted strings with excess arguments', () => {
+    expect(LogBoxLogParser({args: ['%s', 'A', 'B']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: '\ufeff%s B',
+      message: {
+        content: 'A B',
+        substitutions: [
+          {
+            length: 1,
+            offset: 0,
+          },
+        ],
+      },
+    });
+  });
+
+  it('treats "%s" in arguments as literals', () => {
+    expect(LogBoxLogParser({args: ['%s', '%s', 'A']})).toEqual({
+      componentStack: [],
+      stack: [],
+      category: '\ufeff%s A',
+      message: {
+        content: '%s A',
+        substitutions: [
+          {
+            length: 2,
+            offset: 0,
+          },
+        ],
+      },
+    });
+  });
+
+  it('detects a component stack in the second argument', () => {
+    expect(
+      LogBoxLogParser({
+        args: [
+          'Some kind of message',
+          '\n    in MyComponent (at filename.js:1)\n    in MyOtherComponent (at filename2.js:1)',
+        ],
+      }),
+    ).toEqual({
+      componentStack: [
+        {component: 'MyComponent', location: 'filename.js:1'},
+        {component: 'MyOtherComponent', location: 'filename2.js:1'},
+      ],
+      stack: [],
+      category: 'Some kind of message',
+      message: {
+        content: 'Some kind of message',
+        substitutions: [],
+      },
+    });
+  });
+
+  it('does not detect a component stack in the third argument', () => {
+    expect(
+      LogBoxLogParser({
+        args: [
+          'Some kind of message',
+          'Some other kind of message',
+          '\n    in MyComponent (at filename.js:1)\n    in MyOtherComponent (at filename2.js:1)',
+        ],
+      }),
+    ).toEqual({
+      componentStack: [],
+      stack: [],
+      category:
+        'Some kind of message Some other kind of message \n    in MyComponent (at filename.js:1)\n    in MyOtherComponent (at filename2.js:1)',
+      message: {
+        content:
+          'Some kind of message Some other kind of message \n    in MyComponent (at filename.js:1)\n    in MyOtherComponent (at filename2.js:1)',
+        substitutions: [],
+      },
+    });
+  });
+});
diff --git a/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
new file mode 100644
index 00000000000..36dca4a6818
--- /dev/null
+++ b/Libraries/LogBox/Data/__tests__/LogBoxSymbolication-test.js
@@ -0,0 +1,53 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+react_native
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+import type {StackFrame} from '../../../Core/NativeExceptionsManager';
+
+jest.mock('../../../Core/Devtools/symbolicateStackTrace');
+
+const LogBoxSymbolication = require('../LogBoxSymbolication');
+
+const symbolicateStackTrace: JestMockFn<
+  $ReadOnlyArray<Array<StackFrame>>,
+  Promise<Array<StackFrame>>,
+> = (require('../../../Core/Devtools/symbolicateStackTrace'): any);
+
+const createStack = methodNames =>
+  methodNames.map(methodName => ({
+    column: null,
+    file: 'file://path/to/file.js',
+    lineNumber: 1,
+    methodName,
+  }));
+
+describe('LogBoxSymbolication', () => {
+  beforeEach(() => {
+    jest.resetModules();
+    symbolicateStackTrace.mockImplementation(async stack => stack);
+  });
+
+  it('symbolicates different stacks', () => {
+    LogBoxSymbolication.symbolicate(createStack(['A', 'B', 'C']));
+    LogBoxSymbolication.symbolicate(createStack(['D', 'E', 'F']));
+
+    expect(symbolicateStackTrace.mock.calls.length).toBe(2);
+  });
+
+  it('batch symbolicates equivalent stacks', () => {
+    const stack = createStack(['A', 'B', 'C']);
+    LogBoxSymbolication.symbolicate(stack);
+    LogBoxSymbolication.symbolicate(stack);
+
+    expect(symbolicateStackTrace.mock.calls.length).toBe(1);
+  });
+});
diff --git a/Libraries/LogBox/__tests__/LogBox-test.js b/Libraries/LogBox/__tests__/LogBox-test.js
new file mode 100644
index 00000000000..bd51e49f0ff
--- /dev/null
+++ b/Libraries/LogBox/__tests__/LogBox-test.js
@@ -0,0 +1,79 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @emails oncall+react_native
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+const LogBox = require('../LogBox');
+const LogBoxLogData = require('../Data/LogBoxLogData');
+
+declare var console: any;
+
+describe('LogBox', () => {
+  const {error, warn} = console;
+
+  beforeEach(() => {
+    jest.resetModules();
+    console.error = jest.fn();
+    console.warn = jest.fn();
+  });
+
+  afterEach(() => {
+    LogBox.uninstall();
+    console.error = error;
+    console.warn = warn;
+  });
+
+  it('can set `disableLogBox` after installing', () => {
+    expect(console.disableLogBox).toBe(undefined);
+
+    LogBox.install();
+
+    expect(console.disableLogBox).toBe(false);
+    expect(LogBoxLogData.isDisabled()).toBe(false);
+
+    console.disableLogBox = true;
+
+    expect(console.disableLogBox).toBe(true);
+    expect(LogBoxLogData.isDisabled()).toBe(true);
+  });
+
+  it('can set `disableLogBox` before installing', () => {
+    expect(console.disableLogBox).toBe(undefined);
+
+    console.disableLogBox = true;
+    LogBox.install();
+
+    expect(console.disableLogBox).toBe(true);
+    expect(LogBoxLogData.isDisabled()).toBe(true);
+  });
+
+  it('registers warnings', () => {
+    jest.mock('../Data/LogBoxLogData');
+
+    LogBox.install();
+
+    expect(LogBoxLogData.add).not.toBeCalled();
+    console.warn('...');
+    expect(LogBoxLogData.add).toBeCalled();
+  });
+
+  it('registers errors beginning with "Warning: " as warnings', () => {
+    jest.mock('../Data/LogBoxLogData');
+
+    LogBox.install();
+
+    console.error('...');
+    expect(LogBoxLogData.add).not.toBeCalled();
+
+    console.error('Warning: ...');
+    expect(LogBoxLogData.add).toBeCalled();
+  });
+});