diff --git a/.gitignore b/.gitignore
index 97da45fa..f2dbdb60 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,6 +23,7 @@ phpcs.xml.dist
 /source/wp-content/mu-plugins/*
 
 # ...except the actual source of this project.
+!/source/wp-content/tests
 !/source/wp-content/themes
 !/source/wp-content/themes/wporg-main-2022
 !/source/wp-content/mu-plugins
diff --git a/.wp-env.json b/.wp-env.json
index a90954ef..d3a76826 100644
--- a/.wp-env.json
+++ b/.wp-env.json
@@ -28,5 +28,16 @@
 		"wp-content/mu-plugins": "./source/wp-content/mu-plugins",
 		"wp-content/mu-plugins/0-sandbox.php": "./env/0-sandbox.php",
 		"wp-cli.yml": "./wp-cli.yml"
+	},
+	"env": {
+		"tests": {
+			"config": {
+				"WP_ENVIRONMENT_TYPE": false
+			},
+			"mappings": {
+				"wp-content/tests": "./source/wp-content/tests",
+				"vendor": "./vendor"
+			}
+		}
 	}
 }
diff --git a/composer.json b/composer.json
index eb07ef49..23936b5b 100644
--- a/composer.json
+++ b/composer.json
@@ -100,7 +100,8 @@
 		"wpackagist-plugin/wordpress-importer": "*",
 		"wporg/wporg-repo-tools": "dev-trunk",
 		"wporg/wporg-mu-plugins": "dev-build",
-		"wporg/wporg-parent-2021": "dev-build"
+		"wporg/wporg-parent-2021": "dev-build",
+		"yoast/phpunit-polyfills": "^1.0"
 	},
 	"scripts": {
 		"format": "phpcbf -p",
diff --git a/composer.lock b/composer.lock
index b2501792..6fdb599c 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "dbc668c35d44dec32c81c5dce68077a4",
+    "content-hash": "652c9baa4366ca13314c13344b96f9cc",
     "packages": [],
     "packages-dev": [
         {
@@ -2367,12 +2367,12 @@
             "source": {
                 "type": "git",
                 "url": "https://github.com/WordPress/wporg-mu-plugins.git",
-                "reference": "a6217709c8706986582c855a121661178ff685d0"
+                "reference": "ae072f27720086a01364d090077698c81a2efd87"
             },
             "dist": {
                 "type": "zip",
-                "url": "https://api.github.com/repos/WordPress/wporg-mu-plugins/zipball/a6217709c8706986582c855a121661178ff685d0",
-                "reference": "a6217709c8706986582c855a121661178ff685d0",
+                "url": "https://api.github.com/repos/WordPress/wporg-mu-plugins/zipball/ae072f27720086a01364d090077698c81a2efd87",
+                "reference": "ae072f27720086a01364d090077698c81a2efd87",
                 "shasum": ""
             },
             "require-dev": {
@@ -2410,7 +2410,7 @@
                 "source": "https://github.com/WordPress/wporg-mu-plugins/tree/build",
                 "issues": "https://github.com/WordPress/wporg-mu-plugins/issues"
             },
-            "time": "2023-03-29T04:29:54+00:00"
+            "time": "2023-03-31T15:33:47+00:00"
         },
         {
             "name": "wporg/wporg-parent-2021",
@@ -2462,6 +2462,66 @@
                 "source": "https://github.com/WordPress/wporg-repo-tools/tree/trunk"
             },
             "time": "2022-11-16T17:56:26+00:00"
+        },
+        {
+            "name": "yoast/phpunit-polyfills",
+            "version": "1.0.5",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/Yoast/PHPUnit-Polyfills.git",
+                "reference": "3b59adeef77fb1c03ff5381dbb9d68b0aaff3171"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/Yoast/PHPUnit-Polyfills/zipball/3b59adeef77fb1c03ff5381dbb9d68b0aaff3171",
+                "reference": "3b59adeef77fb1c03ff5381dbb9d68b0aaff3171",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=5.4",
+                "phpunit/phpunit": "^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0"
+            },
+            "require-dev": {
+                "yoast/yoastcs": "^2.3.0"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-main": "2.x-dev"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "phpunitpolyfills-autoload.php"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD-3-Clause"
+            ],
+            "authors": [
+                {
+                    "name": "Team Yoast",
+                    "email": "support@yoast.com",
+                    "homepage": "https://yoast.com"
+                },
+                {
+                    "name": "Contributors",
+                    "homepage": "https://github.com/Yoast/PHPUnit-Polyfills/graphs/contributors"
+                }
+            ],
+            "description": "Set of polyfills for changed PHPUnit functionality to allow for creating PHPUnit cross-version compatible tests",
+            "homepage": "https://github.com/Yoast/PHPUnit-Polyfills",
+            "keywords": [
+                "phpunit",
+                "polyfill",
+                "testing"
+            ],
+            "support": {
+                "issues": "https://github.com/Yoast/PHPUnit-Polyfills/issues",
+                "source": "https://github.com/Yoast/PHPUnit-Polyfills"
+            },
+            "time": "2023-03-30T23:39:05+00:00"
         }
     ],
     "aliases": [],
diff --git a/env/export-content/tests/block-parser-test.php b/env/export-content/tests/block-parser-test.php
new file mode 100644
index 00000000..97b86c78
--- /dev/null
+++ b/env/export-content/tests/block-parser-test.php
@@ -0,0 +1,141 @@
+<?php
+/**
+ * Test the BlockParser class and related functions.
+ */
+
+use WordPress_org\Main_2022\ExportToPatterns\BlockParser;
+use function WordPress_org\Main_2022\ExportToPatterns\replace_with_i18n;
+
+require dirname( __DIR__ ) . '/includes/parser.php';
+
+class BlockParser_Test extends WP_UnitTestCase {
+	/**
+	 * Data provider for valid block content, and the expected strings when parsed.
+	 *
+	 * @return array
+	 */
+	public function data_block_content_strings() {
+		return [
+			[
+				// Two plain paragraphs.
+				"<!-- wp:paragraph -->\n<p>One.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Two.</p>\n<!-- /wp:paragraph -->",
+				[ 'One.', 'Two.' ],
+			],
+			[
+				// A paragraph with nested HTML.
+				"<!-- wp:paragraph -->\n<p>A paragraph with <strong>bold</strong> text.</p>\n<!-- /wp:paragraph -->",
+				[ 'A paragraph with <strong>bold</strong> text.' ],
+			],
+			[
+				// A paragraph with a nested link.
+				"<!-- wp:paragraph -->\n<p>A paragraph with <a href=\"#\">a link</strong>.</p>\n<!-- /wp:paragraph -->",
+				[ 'A paragraph with <a href="#">a link</strong>.' ],
+			],
+			[
+				// Empty paragraph.
+				"<!-- wp:paragraph -->\n<p></p>\n<!-- /wp:paragraph -->\n",
+				[],
+			],
+			[
+				// Buttons.
+				"<!-- wp:buttons -->\n<div class=\"wp-block-buttons\"><!-- wp:button -->\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"#\">Button 1</a></div>\n<!-- /wp:button -->\n\n<!-- wp:button -->\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link wp-element-button\" href=\"#\">Button 2</a></div>\n<!-- /wp:button --></div>\n<!-- /wp:buttons -->",
+				[ 'Button 1', 'Button 2' ],
+			],
+			[
+				// Column with a list, list-items.
+				"<!-- wp:column {\"verticalAlignment\":\"center\",\"width\":\"50%\",\"style\":{\"spacing\":{\"padding\":{\"right\":\"60px\"}}}} -->\n<div class=\"wp-block-column is-vertically-aligned-center\" style=\"padding-right:60px;flex-basis:50%\"><!-- wp:list {\"className\":\"is-style-features\"} -->\n<ul class=\"is-style-features\"><!-- wp:list-item -->\n<li>Simple</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Intuitive</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Extendable</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Free</li>\n<!-- /wp:list-item -->\n\n<!-- wp:list-item -->\n<li>Open</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list --></div>\n<!-- /wp:column -->",
+				[ 'Simple', 'Intuitive', 'Extendable', 'Free', 'Open' ],
+			],
+			[
+				// Image block with an alt.
+				"<!-- wp:image {\"width\":150,\"height\":45,\"linkDestination\":\"custom\"} -->\n<figure class=\"wp-block-image is-resized\"><a href=\"#\"><img src=\"./badge-apple.png\" alt=\"Download on the Apple App Store\" width=\"150\" height=\"45\" /></a></figure>\n<!-- /wp:image -->",
+				[ 'Download on the Apple App Store' ],
+			],
+			[
+				// Navigation with custom navigation links.
+				"<!-- wp:navigation {\"textColor\":\"blueberry-1\",\"overlayMenu\":\"never\",\"className\":\"is-style-dots\",\"style\":{\"spacing\":{\"blockGap\":\"0px\"}},\"fontSize\":\"small\"} -->\n<!-- wp:navigation-link {\"label\":\"Releases\",\"url\":\"https://wordpress.org/download/releases/\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n\n<!-- wp:navigation-link {\"label\":\"Nightly\",\"url\":\"https://wordpress.org/download/beta-nightly/\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n\n<!-- wp:navigation-link {\"label\":\"Counter\",\"url\":\"https://wordpress.org/download/counter/\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n\n<!-- wp:navigation-link {\"label\":\"Source\",\"url\":\"https://wordpress.org/download/source/\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n<!-- /wp:navigation -->",
+				[ 'Releases', 'Nightly', 'Counter', 'Source' ],
+			],
+			[
+				// Cover with background image (with alt), and nested paragraph.
+				"<!-- wp:cover {\"url\":\"http://localhost:8878/wp-content/uploads/2022/10/kerstin-wrba-zeInZepl_Hw-unsplash-scaled.jpg\",\"id\":7,\"dimRatio\":50,\"overlayColor\":\"tertiary\",\"isDark\":false} -->\n<div class=\"wp-block-cover is-light\"><span aria-hidden=\"true\" class=\"wp-block-cover__background has-tertiary-background-color has-background-dim\"></span><img class=\"wp-block-cover__image-background wp-image-7\" alt=\"Some alt.\" src=\"http://localhost:8878/wp-content/uploads/2022/10/kerstin-wrba-zeInZepl_Hw-unsplash-scaled.jpg\" data-object-fit=\"cover\"/><div class=\"wp-block-cover__inner-container\"><!-- wp:paragraph {\"align\":\"center\",\"fontSize\":\"large\"} -->\n<p class=\"has-text-align-center has-large-font-size\">Testing a Cover</p>\n<!-- /wp:paragraph --></div></div>\n<!-- /wp:cover -->",
+				[ 'Some alt.', 'Testing a Cover' ],
+			],
+			[
+				// Social links.
+				"<!-- wp:social-links {\"className\":\"is-style-logos-only\"} -->\n<ul class=\"wp-block-social-links is-style-logos-only\">\n<!-- wp:social-link {\"url\":\"https://www.facebook.com/WordPress/\",\"service\":\"facebook\",\"label\":\"Visit our Facebook page\"} /-->\n<!-- wp:social-link {\"url\":\"https://twitter.com/WordPress\",\"service\":\"twitter\",\"label\":\"Visit our Twitter account\"} /-->\n</ul>\n<!-- /wp:social-links -->",
+				[ 'Visit our Facebook page', 'Visit our Twitter account' ],
+			],
+			[
+				// List with links
+				"<!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li><a href=\"#\">Fonts API</a></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Interactivity <a href=\"#\">Link</a> API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><a href=\"\">Block API</a></li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->",
+				[ 'Fonts API', 'Interactivity <a href="#">Link</a> API', 'Block API' ],
+			],
+			[
+				// List of lists
+				"<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>APIs:<!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li>Fonts API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Interactivity API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Block API</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list --></li>\n<!-- /wp:list-item -->\n</ul>\n<!-- /wp:list -->",
+				[ 'APIs:', 'Fonts API', 'Interactivity API', 'Block API' ],
+			],
+		];
+	}
+
+	/**
+	 * Test string parsing from valid block content.
+	 *
+	 * @dataProvider data_block_content_strings
+	 */
+	public function test_strings_parser( $block_content, $expected ) {
+		$parser = new BlockParser( $block_content );
+		$strings = $parser->to_strings();
+		$this->assertSame( $expected, $strings );
+	}
+
+	/**
+	 * Data provider for valid block content and the i18n-ized results.
+	 *
+	 * @return array
+	 */
+	public function data_block_content_i18n() {
+		return [
+			[
+				// Two plain paragraphs.
+				"<!-- wp:paragraph -->\n<p>One.</p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p>Two.</p>\n<!-- /wp:paragraph -->",
+				"<!-- wp:paragraph -->\n<p><?php _e( 'One.', 'wporg' ); ?></p>\n<!-- /wp:paragraph -->\n\n<!-- wp:paragraph -->\n<p><?php _e( 'Two.', 'wporg' ); ?></p>\n<!-- /wp:paragraph -->",
+			],
+			[
+				// Image block with an alt.
+				"<!-- wp:image {\"width\":150,\"height\":45,\"linkDestination\":\"custom\"} -->\n<figure class=\"wp-block-image is-resized\"><a href=\"#\"><img src=\"./badge-apple.png\" alt=\"Download on the Apple App Store\" width=\"150\" height=\"45\" /></a></figure>\n<!-- /wp:image -->",
+				"<!-- wp:image {\"width\":150,\"height\":45,\"linkDestination\":\"custom\"} -->\n<figure class=\"wp-block-image is-resized\"><a href=\"#\"><img src=\"./badge-apple.png\" alt=\"<?php _e( 'Download on the Apple App Store', 'wporg' ); ?>\" width=\"150\" height=\"45\" /></a></figure>\n<!-- /wp:image -->",
+			],
+			[
+				// Navigation with custom navigation links.
+				"<!-- wp:navigation {\"textColor\":\"blueberry-1\",\"overlayMenu\":\"never\",\"className\":\"is-style-dots\",\"style\":{\"spacing\":{\"blockGap\":\"0px\"}},\"fontSize\":\"small\"} -->\n<!-- wp:navigation-link {\"label\":\"Releases\",\"url\":\"#\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n<!-- /wp:navigation -->",
+				"<!-- wp:navigation {\"textColor\":\"blueberry-1\",\"overlayMenu\":\"never\",\"className\":\"is-style-dots\",\"style\":{\"spacing\":{\"blockGap\":\"0px\"}},\"fontSize\":\"small\"} -->\n<!-- wp:navigation-link {\"label\":\"<?php _e( 'Releases', 'wporg' ); ?>\",\"url\":\"#\",\"kind\":\"custom\",\"isTopLevelLink\":true} /-->\n<!-- /wp:navigation -->",
+			],
+			[
+				// List with links
+				"<!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li><a href=\"#\">Fonts API</a></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Interactivity <a href=\"#\">Link</a> API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><a href=\"\">Block API</a></li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->",
+				"<!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li><a href=\"#\"><?php _e( 'Fonts API', 'wporg' ); ?></a></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><?php _e( 'Interactivity <a href=\"#\">Link</a> API', 'wporg' ); ?></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><a href=\"\"><?php _e( 'Block API', 'wporg' ); ?></a></li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list -->",
+			],
+			[
+				// List of lists
+				"<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li>APIs:<!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li>Fonts API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Interactivity API</li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li>Block API</li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list --></li>\n<!-- /wp:list-item -->\n</ul>\n<!-- /wp:list -->\n",
+				"<!-- wp:list -->\n<ul><!-- wp:list-item -->\n<li><?php _e( 'APIs:', 'wporg' ); ?><!-- wp:list -->\n<ul>\n<!-- wp:list-item -->\n<li><?php _e( 'Fonts API', 'wporg' ); ?></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><?php _e( 'Interactivity API', 'wporg' ); ?></li>\n<!-- /wp:list-item -->\n<!-- wp:list-item -->\n<li><?php _e( 'Block API', 'wporg' ); ?></li>\n<!-- /wp:list-item --></ul>\n<!-- /wp:list --></li>\n<!-- /wp:list-item -->\n</ul>\n<!-- /wp:list -->\n",
+			],
+			[
+				"<!-- wp:quote -->\n<blockquote class=\"wp-block-quote\"><!-- wp:paragraph -->\m<p>I'm interested in running the open-source WordPress &lt;https://wordpress.org/&gt; web software and I was wondering if my account supported the following:</p>\n<!-- /wp:paragraph --></blockquote>\n<!-- /wp:quote -->",
+				"<!-- wp:quote -->\n<blockquote class=\"wp-block-quote\"><!-- wp:paragraph -->\m<p><?php _e( 'I&#039;m interested in running the open-source WordPress &lt;https://wordpress.org/&gt; web software and I was wondering if my account supported the following:', 'wporg' ); ?></p>\n<!-- /wp:paragraph --></blockquote>\n<!-- /wp:quote -->",
+			],
+		];
+	}
+
+	/**
+	 * Test the i18n replacement.
+	 *
+	 * @dataProvider data_block_content_i18n
+	 */
+	public function test_i18n_replacement( $block_content, $expected ) {
+		$content_with_i18n = replace_with_i18n( $block_content );
+		$this->assertSame( $expected, $content_with_i18n );
+	}
+}
diff --git a/package.json b/package.json
index c036c987..54cbe512 100644
--- a/package.json
+++ b/package.json
@@ -26,7 +26,8 @@
 		"build:theme": "yarn workspace wporg-main-2022-theme build",
 		"lint:frontend": "yarn workspace wporg-main-2022-theme lint:css && yarn workspace wporg-main-2022-theme lint:js",
 		"lint:php": "composer run lint source/wp-content/themes/wporg-main-2022 source/wp-content/mu-plugins/theme-switcher.php env",
-		"start:theme": "yarn workspace wporg-main-2022-theme start"
+		"start:theme": "yarn workspace wporg-main-2022-theme start",
+		"test:php": "wp-env run phpunit 'WP_MULTISITE=1 phpunit -c /var/www/html/wp-content/tests/phpunit/phpunit.xml --verbose'"
 	},
 	"workspaces": [
 		"source/wp-content/themes/wporg-main-2022"
diff --git a/source/wp-content/tests/phpunit/bootstrap.php b/source/wp-content/tests/phpunit/bootstrap.php
new file mode 100644
index 00000000..2d4525f3
--- /dev/null
+++ b/source/wp-content/tests/phpunit/bootstrap.php
@@ -0,0 +1,44 @@
+<?php
+/**
+ * PHPUnit bootstrap file
+ */
+
+// Require composer dependencies.
+require_once __DIR__ . '/../../../vendor/autoload.php';
+
+// Detect where to load the WordPress tests environment from.
+if ( false !== getenv( 'WP_TESTS_DIR' ) ) {
+	$_test_root = getenv( 'WP_TESTS_DIR' );
+} else {
+	$_test_root = __DIR__ . '/../../../vendor/wp-phpunit/wp-phpunit';
+}
+
+// Give access to tests_add_filter() function.
+require_once $_test_root . '/includes/functions.php';
+
+/**
+ * Adds a wp_die handler for use during tests.
+ *
+ * If bootstrap.php triggers wp_die, it will not cause the script to fail. This
+ * means that tests will look like they passed even though they should have
+ * failed. So we throw an exception if WordPress dies during test setup. This
+ * way the failure is observable.
+ *
+ * @param string|WP_Error $message The error message.
+ *
+ * @throws Exception When a `wp_die()` occurs.
+ */
+function fail_if_died( $message ) {
+	if ( is_wp_error( $message ) ) {
+		$message = $message->get_error_message();
+	}
+
+	throw new Exception( 'WordPress died: ' . $message );
+}
+tests_add_filter( 'wp_die_handler', 'fail_if_died' );
+
+// Start up the WP testing environment.
+require_once $_test_root . '/includes/bootstrap.php';
+
+// Use existing behavior for wp_die during actual test execution.
+remove_filter( 'wp_die_handler', 'fail_if_died' );
diff --git a/source/wp-content/tests/phpunit/phpunit.xml b/source/wp-content/tests/phpunit/phpunit.xml
new file mode 100644
index 00000000..fcda9e0b
--- /dev/null
+++ b/source/wp-content/tests/phpunit/phpunit.xml
@@ -0,0 +1,14 @@
+<phpunit
+		bootstrap="./bootstrap.php"
+		backupGlobals="false"
+		colors="true"
+		convertErrorsToExceptions="true"
+		convertNoticesToExceptions="true"
+		convertWarningsToExceptions="true"
+>
+	<testsuites>
+		<testsuite name="export-content">
+			<directory suffix="-test.php">../../../env/export-content/tests</directory>
+		</testsuite>
+	</testsuites>
+</phpunit>