jest: Prepare for eslint-plugin-jest upgrade.

A few occurrences of these rules will newly be flagged with the
upcoming `eslint-plugin-jest` upgrade:

jest/expect-expect:
  https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/expect-expect.md

jest/no-try-expect
  https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/no-try-expect.md

jest/no-standalone-expect
  https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/no-standalone-expect.md

Adapt to the first two and disable the third, which seems unhelpful,
as noted in code comments. It did, however, lead to an improvement
in `sentry-test`, where we move some `expect`s from `beforeEach` and
`afterEach` into the tests themselves, since logically they're part
of the tests themselves [1].

[1] zulip#4235 (comment)

.eslintrc.yaml

@@ -169,6 +169,18 @@ rules:
   # see jest-community/eslint-plugin-jest#203 (rule might be removed?)
   jest/valid-describe: off
 
+  # The docs for this rule [1] say that placing an `expect` call
+  # outside a `test` or `it` block (e.g., in a `beforeEach` or
+  # `afterEach`) means that the assertion isn't executed. Empirically,
+  # this seems just wrong [2], and there are a few places where we
+  # want to call `expect` in a `beforeEach` or `afterEach` to assert
+  # that multiple tests in the same file aren't interfering with each
+  # other by leaving bits of state lying around.
+  #
+  # [1] https://github.com/jest-community/eslint-plugin-jest/blob/master/docs/rules/no-standalone-expect.md
+  # [2] https://github.com/zulip/zulip-mobile/pull/4235#discussion_r489984717
+  jest/no-standalone-expect: off
+
   # React
   react/jsx-filename-extension: off  # Like RN upstream, we call the files *.js.
   react/destructuring-assignment: off  # The opposite is often much cleaner.

src/__tests__/sentry-test.js

@@ -7,28 +7,25 @@ describe('sentry', () => {
   describe('is usable without initialization', () => {
     // Sentry shouldn't be active at all in debug mode -- certainly not while
     // we're specifically testing that its entry points can be used while it's
-    // uninitialized.
-    beforeEach(() => {
-      expect(isSentryActive()).toBeFalse();
-    });
-
-    afterEach(() => {
-      expect(isSentryActive()).toBeFalse();
-    });
+    // uninitialized. These tests assert that.
 
     test('breadcrumbs', () => {
+      expect(isSentryActive()).toBeFalse();
       Sentry.addBreadcrumb({
         message: 'test message',
         level: Sentry.Severity.Debug,
       });
+      expect(isSentryActive()).toBeFalse();
     });
 
     test('exception reporting', () => {
+      expect(isSentryActive()).toBeFalse();
       // The text here is intended to prevent some hypothetical future reader of
       // Sentry event logs dismissing the error as harmless expected noise, in
       // case Sentry is somehow actually initialized at this point.
       const err = new Error('Jest test error; should not result in a Sentry event');
       Sentry.captureException(err);
+      expect(isSentryActive()).toBeFalse();
     });
   });
 });

src/emoji/__tests__/data-test.js

@@ -7,6 +7,9 @@ import { codeToEmojiMap, getFilteredEmojis } from '../data';
 
 /* eslint-disable no-multi-spaces */
 describe('codeToEmojiMap', () => {
+  // Tell Jest to recognize `check` as a helper function that runs
+  // assertions.
+  /* eslint jest/expect-expect: ["error", { "assertFunctionNames": ["expect", "check"] }] */
   const check = (name, string1, string2) => {
     expect(string1).toEqual(string2);
     expect(codeToEmojiMap[name]).toEqual(string1);

src/message/__tests__/fetchActions-test.js

@@ -202,15 +202,14 @@ describe('fetchActions', () => {
         };
         fetch.mockResponseSuccess(JSON.stringify(response));
 
-        expect.assertions(2);
-        try {
-          await store.dispatch(
+        await expect(
+          store.dispatch(
             fetchMessages({ narrow: HOME_NARROW, anchor: 0, numBefore: 1, numAfter: 1 }),
-          );
-        } catch (e) {
+          ),
+        ).rejects.toThrow(
           // Update this with changes to the message string or error type.
-          expect(e.message).toBe('Active account not logged in');
-        }
+          new Error('Active account not logged in'),
+        );
 
         const actions = store.getActions();
 
@@ -255,15 +254,14 @@ describe('fetchActions', () => {
         };
         fetch.mockResponseSuccess(JSON.stringify(response));
 
-        expect.assertions(2);
-        try {
-          await store.dispatch(
+        await expect(
+          store.dispatch(
             fetchMessages({ narrow: HOME_NARROW, anchor: 0, numBefore: 1, numAfter: 1 }),
-          );
-        } catch (e) {
+          ),
+        ).rejects.toThrow(
           // Update this with changes to the error type.
-          expect(e).toBeInstanceOf(TypeError);
-        }
+          TypeError,
+        );
 
         const actions = store.getActions();
 
@@ -281,14 +279,11 @@ describe('fetchActions', () => {
 
         fetch.mockResponseFailure(fetchError);
 
-        expect.assertions(1);
-        try {
-          await store.dispatch(
+        await expect(
+          store.dispatch(
             fetchMessages({ narrow: HOME_NARROW, anchor: 0, numBefore: 1, numAfter: 1 }),
-          );
-        } catch (e) {
-          expect(e).toBe(fetchError);
-        }
+          ),
+        ).rejects.toThrow(fetchError);
       });
     });
 

src/utils/__tests__/internalLinks-test.js

@@ -1,4 +1,8 @@
 /* @flow strict-local */
+// Tell Jest to recognize `expectStream` as a helper function that
+// runs assertions.
+/* eslint jest/expect-expect: ["error", { "assertFunctionNames": ["expect", "expectStream"] }] */
+
 import type { User } from '../../api/modelTypes';
 import { streamNarrow, topicNarrow, groupNarrow, STARRED_NARROW } from '../narrow';
 import {