Separated the snapshot summary creation from the printing to improve testability.

packages/jest-cli/src/reporters/__tests__/__snapshots__/get_snapshot_summary.test.js.snap

@@ -0,0 +1,40 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`creates a snapshot summary 1`] = `
+Array [
+  "<bold>Snapshot Summary",
+  "<bold><green> › 1 snapshot</> written in 1 test suite.",
+  "<bold><red> › 1 snapshot test</> failed in 1 test suite. <dim>Inspect your code changes or press --u to update them.",
+  "<bold><green> › 1 snapshot</> updated in 1 test suite.",
+  "<bold><red> › 1 obsolete snapshot file</> found, press --u to remove it.",
+  "<bold><red> › 1 obsolete snapshot</> found, press --u to remove it.",
+]
+`;
+
+exports[`creates a snapshot summary after an update 1`] = `
+Array [
+  "<bold>Snapshot Summary",
+  "<bold><green> › 1 snapshot</> written in 1 test suite.",
+  "<bold><red> › 1 snapshot test</> failed in 1 test suite. <dim>Inspect your code changes or press --u to update them.",
+  "<bold><green> › 1 snapshot</> updated in 1 test suite.",
+  "<bold><red> › 1 obsolete snapshot file</> removed.",
+  "<bold><red> › 1 obsolete snapshot</> removed.",
+]
+`;
+
+exports[`creates a snapshot summary with multiple snapshot being written/updated 1`] = `
+Array [
+  "<bold>Snapshot Summary",
+  "<bold><green> › 2 snapshots</> written in 2 test suites.",
+  "<bold><red> › 2 snapshot tests</> failed in 2 test suites. <dim>Inspect your code changes or press --u to update them.",
+  "<bold><green> › 2 snapshots</> updated in 2 test suites.",
+  "<bold><red> › 2 obsolete snapshot files</> found, press --u to remove them..",
+  "<bold><red> › 2 obsolete snapshots</> found, press --u to remove them.",
+]
+`;
+
+exports[`returns nothing if there are no updates 1`] = `
+Array [
+  "<bold>Snapshot Summary",
+]
+`;

packages/jest-cli/src/reporters/__tests__/get_snapshot_summary.test.js

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2017-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+'use strict';
+
+import getSnapshotSummary from '../get_snapshot_summary';
+
+const UPDATE_COMMAND = 'press --u';
+
+test('creates a snapshot summary', () => {
+  const snapshots = {
+    added: 1,
+    didUpdate: false,
+    filesAdded: 1,
+    filesRemoved: 1,
+    filesUnmatched: 1,
+    filesUpdated: 1,
+    matched: 2,
+    total: 2,
+    unchecked: 1,
+    unmatched: 1,
+    updated: 1,
+  };
+
+  expect(getSnapshotSummary(snapshots, UPDATE_COMMAND)).toMatchSnapshot();
+});
+
+test('creates a snapshot summary after an update', () => {
+  const snapshots = {
+    added: 1,
+    didUpdate: true,
+    filesAdded: 1,
+    filesRemoved: 1,
+    filesUnmatched: 1,
+    filesUpdated: 1,
+    unchecked: 1,
+    unmatched: 1,
+    updated: 1,
+  };
+
+  expect(getSnapshotSummary(snapshots, UPDATE_COMMAND)).toMatchSnapshot();
+});
+
+it('creates a snapshot summary with multiple snapshot being written/updated', () => {
+  const snapshots = {
+    added: 2,
+    didUpdate: false,
+    filesAdded: 2,
+    filesRemoved: 2,
+    filesUnmatched: 2,
+    filesUpdated: 2,
+    unchecked: 2,
+    unmatched: 2,
+    updated: 2,
+  };
+
+  expect(getSnapshotSummary(snapshots, UPDATE_COMMAND)).toMatchSnapshot();
+});
+
+it('returns nothing if there are no updates', () => {
+  const snapshots = {
+    added: 0,
+    didUpdate: false,
+    filesAdded: 0,
+    filesRemoved: 0,
+    filesUnmatched: 0,
+    filesUpdated: 0,
+    unchecked: 0,
+    unmatched: 0,
+    updated: 0,
+  };
+  expect(getSnapshotSummary(snapshots, UPDATE_COMMAND)).toMatchSnapshot();
+});

packages/jest-cli/src/reporters/get_snapshot_summary.js

@@ -0,0 +1,84 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+import type {SnapshotSummary} from 'types/TestResult';
+
+import chalk from 'chalk';
+import {pluralize} from './utils';
+
+const ARROW = ' \u203A ';
+const FAIL_COLOR = chalk.bold.red;
+const SNAPSHOT_ADDED = chalk.bold.green;
+const SNAPSHOT_NOTE = chalk.dim;
+const SNAPSHOT_REMOVED = chalk.bold.red;
+const SNAPSHOT_SUMMARY = chalk.bold;
+const SNAPSHOT_UPDATED = chalk.bold.green;
+
+module.exports = (
+  snapshots: SnapshotSummary,
+  updateCommand: string,
+): Array<string> => {
+  const summary = [];
+  summary.push(SNAPSHOT_SUMMARY('Snapshot Summary'));
+  if (snapshots.added) {
+    summary.push(
+      SNAPSHOT_ADDED(ARROW + pluralize('snapshot', snapshots.added)) +
+        ` written in ${pluralize('test suite', snapshots.filesAdded)}.`,
+    );
+  }
+
+  if (snapshots.unmatched) {
+    summary.push(
+      FAIL_COLOR(ARROW + pluralize('snapshot test', snapshots.unmatched)) +
+        ` failed in ` +
+        `${pluralize('test suite', snapshots.filesUnmatched)}. ` +
+        SNAPSHOT_NOTE(
+          'Inspect your code changes or ' + updateCommand + ' to update them.',
+        ),
+    );
+  }
+
+  if (snapshots.updated) {
+    summary.push(
+      SNAPSHOT_UPDATED(ARROW + pluralize('snapshot', snapshots.updated)) +
+        ` updated in ${pluralize('test suite', snapshots.filesUpdated)}.`,
+    );
+  }
+
+  if (snapshots.filesRemoved) {
+    summary.push(
+      SNAPSHOT_REMOVED(
+        ARROW + pluralize('obsolete snapshot file', snapshots.filesRemoved),
+      ) +
+        (snapshots.didUpdate
+          ? ' removed.'
+          : ' found, ' +
+            updateCommand +
+            ' to remove ' +
+            (snapshots.filesRemoved === 1 ? 'it' : 'them.') +
+            '.'),
+    );
+  }
+
+  if (snapshots.unchecked) {
+    summary.push(
+      FAIL_COLOR(ARROW + pluralize('obsolete snapshot', snapshots.unchecked)) +
+        (snapshots.didUpdate
+          ? ' removed.'
+          : ' found, ' +
+            updateCommand +
+            ' to remove ' +
+            (snapshots.filesRemoved === 1 ? 'it' : 'them') +
+            '.'),
+    );
+  }
+
+  return summary;
+};

packages/jest-cli/src/reporters/summary_reporter.js

@@ -15,17 +15,11 @@ import type {ReporterOnStartOptions} from 'types/Reporters';
 
 import chalk from 'chalk';
 import BaseReporter from './base_reporter';
-import {getSummary, pluralize} from './utils';
+import {getSummary} from './utils';
 import getResultHeader from './get_result_header';
+import getSnapshotSummary from './get_snapshot_summary';
 import testPathPatternToRegExp from '../test_path_pattern_to_regexp';
 
-const ARROW = ' \u203A ';
-const FAIL_COLOR = chalk.bold.red;
-const SNAPSHOT_ADDED = chalk.bold.green;
-const SNAPSHOT_NOTE = chalk.dim;
-const SNAPSHOT_REMOVED = chalk.bold.red;
-const SNAPSHOT_SUMMARY = chalk.bold;
-const SNAPSHOT_UPDATED = chalk.bold.green;
 const TEST_SUMMARY_THRESHOLD = 20;
 
 const NPM_EVENTS = new Set([
@@ -149,63 +143,8 @@ class SummaryReporter extends BaseReporter {
         updateCommand = 're-run with `-u`';
       }
 
-      this.log(SNAPSHOT_SUMMARY('Snapshot Summary'));
-      if (snapshots.added) {
-        this.log(
-          SNAPSHOT_ADDED(ARROW + pluralize('snapshot', snapshots.added)) +
-            ` written in ${pluralize('test suite', snapshots.filesAdded)}.`,
-        );
-      }
-
-      if (snapshots.unmatched) {
-        this.log(
-          FAIL_COLOR(ARROW + pluralize('snapshot test', snapshots.unmatched)) +
-            ` failed in ` +
-            `${pluralize('test suite', snapshots.filesUnmatched)}. ` +
-            SNAPSHOT_NOTE(
-              'Inspect your code changes or ' +
-                updateCommand +
-                ' to update them.',
-            ),
-        );
-      }
-
-      if (snapshots.updated) {
-        this.log(
-          SNAPSHOT_UPDATED(ARROW + pluralize('snapshot', snapshots.updated)) +
-            ` updated in ${pluralize('test suite', snapshots.filesUpdated)}.`,
-        );
-      }
-
-      if (snapshots.filesRemoved) {
-        this.log(
-          SNAPSHOT_REMOVED(
-            ARROW + pluralize('obsolete snapshot file', snapshots.filesRemoved),
-          ) +
-            (snapshots.didUpdate
-              ? ' removed.'
-              : ' found, ' +
-                updateCommand +
-                ' to remove ' +
-                (snapshots.filesRemoved === 1 ? 'it' : 'them.') +
-                '.'),
-        );
-      }
-
-      if (snapshots.unchecked) {
-        this.log(
-          FAIL_COLOR(
-            ARROW + pluralize('obsolete snapshot', snapshots.unchecked),
-          ) +
-            (snapshots.didUpdate
-              ? ' removed.'
-              : ' found, ' +
-                updateCommand +
-                ' to remove ' +
-                (snapshots.filesRemoved === 1 ? 'it' : 'them') +
-                '.'),
-        );
-      }
+      const snapshotSummary = getSnapshotSummary(snapshots, updateCommand);
+      snapshotSummary.forEach(this.log);
 
       this.log(''); // print empty line
     }