diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
new file mode 100644
index 0000000..0bc1c9a
--- /dev/null
+++ b/.github/workflows/lint.yml
@@ -0,0 +1,76 @@
+name: Code Quality
+
+on:
+  push:
+    branches: [ master, develop ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  phpcs:
+    name: PHP CodeSniffer
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: '8.1'
+        tools: cs2pr
+
+    - name: Install dependencies
+      run: |
+        composer global require "squizlabs/php_codesniffer=*"
+        composer global require "wp-coding-standards/wpcs=*"
+        composer global require "phpcompatibility/phpcompatibility-wp=*"
+
+    - name: Configure PHPCS
+      run: |
+        phpcs --config-set installed_paths ~/.composer/vendor/wp-coding-standards/wpcs,~/.composer/vendor/phpcompatibility/phpcompatibility-wp
+        phpcs --config-set default_standard WordPress
+
+    - name: Run PHPCS
+      run: |
+        phpcs --standard=WordPress --extensions=php --ignore=scssphp/,tests/,bin/ --report=checkstyle . | cs2pr
+
+  phpstan:
+    name: PHPStan Analysis
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: '8.1'
+
+    - name: Install dependencies
+      run: |
+        composer global require phpstan/phpstan
+
+    - name: Create PHPStan config
+      run: |
+        cat > phpstan.neon << EOF
+        parameters:
+            level: 5
+            paths:
+                - wp-scss.php
+                - options.php
+                - class/
+            excludePaths:
+                - scssphp/
+                - tests/
+            ignoreErrors:
+                # WordPress functions might not be recognized
+                - '#Function (get_option|update_option|add_option|wp_kses|sanitize_text_field) not found#'
+                - '#Function (get_stylesheet_directory|get_template_directory|wp_get_upload_dir) not found#'
+                - '#Function (add_action|add_filter|apply_filters) not found#'
+        EOF
+
+    - name: Run PHPStan
+      run: phpstan analyse --no-progress --error-format=github
\ No newline at end of file
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..348adfa
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,68 @@
+name: Tests
+
+on:
+  push:
+    branches: [ master, develop ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    
+    strategy:
+      matrix:
+        php: ['7.2', '7.3', '7.4', '8.0', '8.1', '8.2']
+        wordpress: ['latest', '6.0', '5.9']
+        exclude:
+          # Exclude PHP 8.2 with older WordPress versions that don't support it
+          - php: '8.2'
+            wordpress: '5.9'
+          - php: '8.2'
+            wordpress: '6.0'
+
+    name: PHP ${{ matrix.php }} / WordPress ${{ matrix.wordpress }}
+
+    services:
+      mysql:
+        image: mysql:8.0
+        env:
+          MYSQL_ROOT_PASSWORD: password
+          MYSQL_DATABASE: wp_scss_test
+        ports:
+          - 3306:3306
+        options: --health-cmd="mysqladmin ping" --health-interval=10s --health-timeout=5s --health-retries=3
+
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+
+    - name: Setup PHP
+      uses: shivammathur/setup-php@v2
+      with:
+        php-version: ${{ matrix.php }}
+        extensions: dom, curl, libxml, mbstring, zip, pcntl, pdo, sqlite, pdo_sqlite, mysql, mysqli, pdo_mysql, bcmath, soap, intl, gd, exif, iconv, imagick
+        coverage: none
+
+    - name: Install WordPress test suite
+      run: |
+        bash bin/install-wp-tests.sh wp_scss_test root password 127.0.0.1:3306 ${{ matrix.wordpress }}
+
+    - name: Run tests
+      run: |
+        cd $GITHUB_WORKSPACE
+        phpunit
+
+    - name: Run tests with coverage (PHP 8.1 only)
+      if: matrix.php == '8.1' && matrix.wordpress == 'latest'
+      run: |
+        cd $GITHUB_WORKSPACE
+        phpunit --coverage-clover=coverage.xml
+
+    - name: Upload coverage to Codecov
+      if: matrix.php == '8.1' && matrix.wordpress == 'latest'
+      uses: codecov/codecov-action@v3
+      with:
+        file: ./coverage.xml
+        flags: unittests
+        name: codecov-umbrella
\ No newline at end of file
diff --git a/README-TESTING.md b/README-TESTING.md
new file mode 100644
index 0000000..651ec2e
--- /dev/null
+++ b/README-TESTING.md
@@ -0,0 +1,120 @@
+# Testing WP-SCSS Plugin
+
+This document explains how to run tests for the WP-SCSS plugin to ensure the settings persistence bug fix and other functionality work correctly.
+
+## Test Setup
+
+### Prerequisites
+
+1. **PHP 7.2+** (same as plugin requirement)
+2. **MySQL/MariaDB** for test database
+3. **PHPUnit** (automatically installed with WordPress test suite)
+
+### Installation
+
+1. **Install WordPress Test Suite:**
+   ```bash
+   # Run from plugin root directory
+   bin/install-wp-tests.sh wp_scss_test root password localhost latest
+   ```
+   
+   Replace the database credentials as needed:
+   - `wp_scss_test` - test database name (will be created)
+   - `root` - database user
+   - `password` - database password  
+   - `localhost` - database host
+
+2. **Verify Setup:**
+   ```bash
+   # Check if test environment is ready
+   ls /tmp/wordpress-tests-lib/
+   ```
+
+## Running Tests
+
+### Run All Tests
+```bash
+phpunit
+```
+
+### Run Specific Test Files
+```bash
+# Test only settings functionality
+phpunit tests/test-settings.php
+
+# Test only integration scenarios
+phpunit tests/test-wp-scss-integration.php
+```
+
+### Run Specific Test Methods
+```bash
+# Test the specific bug fix
+phpunit --filter test_bug_fix_all_settings_preserved
+
+# Test base location change scenario
+phpunit --filter test_base_location_change_persistence
+```
+
+## Test Coverage
+
+### Settings Sanitization Tests (`test-settings.php`)
+
+- **test_sanitize_preserves_all_fields** - Ensures all 9 form fields are preserved
+- **test_sanitize_adds_trailing_slashes** - Verifies directory path formatting
+- **test_sanitize_checkbox_fields** - Tests checkbox handling (checked/unchecked)
+- **test_sanitize_handles_empty_fields** - Tests behavior with missing data
+- **test_sanitize_text_fields** - Tests XSS protection via sanitize_text_field()
+- **test_bug_fix_all_settings_preserved** - Regression test for the original bug
+
+### Integration Tests (`test-wp-scss-integration.php`)
+
+- **test_settings_persistence_workflow** - Full save/retrieve cycle
+- **test_base_location_change_persistence** - Specific bug scenario reproduction
+- **test_development_mode_persistence** - Development settings scenarios
+- **test_checkbox_form_behavior** - Real WordPress checkbox behavior
+- **test_old_sanitize_method_would_fail** - Proves the bug was actually fixed
+
+## The Bug We Fixed
+
+**Original Problem:** The `sanitize()` method only preserved `scss_dir` and `css_dir` fields, causing all other settings (base location, compilation mode, etc.) to be lost on save.
+
+**Tests That Prove the Fix:**
+- `test_bug_fix_all_settings_preserved` - Shows all 9 fields are now saved
+- `test_base_location_change_persistence` - Reproduces exact user scenario
+- `test_old_sanitize_method_would_fail` - Demonstrates the old broken behavior
+
+## Test Database
+
+Tests use a separate database (`wp_scss_test` by default) that is:
+- Automatically created by the install script
+- Cleaned between test runs
+- Completely separate from your development/production WordPress
+
+## Continuous Integration
+
+These tests can be integrated into CI/CD pipelines:
+
+```yaml
+# Example GitHub Actions workflow
+- name: Setup test database
+  run: |
+    sudo systemctl start mysql
+    bin/install-wp-tests.sh wp_scss_test root password localhost latest
+
+- name: Run tests
+  run: phpunit
+```
+
+## Troubleshooting
+
+**"Could not find wp-tests-config.php"**
+- Run the install script: `bin/install-wp-tests.sh ...`
+
+**Database connection errors**
+- Verify MySQL is running
+- Check database credentials in install command
+- Ensure database user has CREATE privileges
+
+**Class not found errors**
+- Ensure you're running tests from the plugin root directory
+- Check that wp-scss.php and options.php exist
\ No newline at end of file
diff --git a/bin/install-wp-tests.sh b/bin/install-wp-tests.sh
new file mode 100755
index 0000000..a4a2fcf
--- /dev/null
+++ b/bin/install-wp-tests.sh
@@ -0,0 +1,147 @@
+#!/usr/bin/env bash
+
+if [ $# -lt 3 ]; then
+	echo "usage: $0 <db-name> <db-user> <db-pass> [db-host] [wp-version] [skip-database-creation]"
+	exit 1
+fi
+
+DB_NAME=$1
+DB_USER=$2
+DB_PASS=$3
+DB_HOST=${4-localhost}
+WP_VERSION=${5-latest}
+SKIP_DB_CREATE=${6-false}
+
+TMPDIR=${TMPDIR-/tmp}
+TMPDIR=$(echo $TMPDIR | sed -e "s/\/$//")
+WP_TESTS_DIR=${WP_TESTS_DIR-$TMPDIR/wordpress-tests-lib}
+WP_CORE_DIR=${WP_CORE_DIR-$TMPDIR/wordpress/}
+
+download() {
+    if [ `which curl` ]; then
+        curl -s "$1" > "$2";
+    elif [ `which wget` ]; then
+        wget -nv -O "$2" "$1"
+    fi
+}
+
+if [[ $WP_VERSION =~ ^[0-9]+\.[0-9]+$ ]]; then
+	WP_TESTS_TAG="branches/$WP_VERSION"
+elif [[ $WP_VERSION =~ [0-9]+\.[0-9]+\.[0-9]+ ]]; then
+	if [[ $WP_VERSION =~ [0-9]+\.[0-9]+\.[0] ]]; then
+		# version x.x.0 means the first release of the major version, so strip off the .0 and download version x.x
+		WP_TESTS_TAG="tags/${WP_VERSION%??}"
+	else
+		WP_TESTS_TAG="tags/$WP_VERSION"
+	fi
+elif [[ $WP_VERSION == 'nightly' || $WP_VERSION == 'trunk' ]]; then
+	WP_TESTS_TAG="trunk"
+else
+	# http serves a single offer, whereas https serves multiple. we only want one
+	download http://api.wordpress.org/core/version-check/1.7/ /tmp/wp-latest.json
+	grep '[0-9]+\.[0-9]+(\.[0-9]+)?' /tmp/wp-latest.json
+	LATEST_VERSION=$(grep -o '"version":"[^"]*' /tmp/wp-latest.json | sed 's/"version":"//')
+	if [[ -z "$LATEST_VERSION" ]]; then
+		echo "Latest WordPress version could not be found"
+		exit 1
+	fi
+	WP_TESTS_TAG="tags/$LATEST_VERSION"
+fi
+
+set -ex
+
+install_wp() {
+
+	if [ -d $WP_CORE_DIR ]; then
+		return;
+	fi
+
+	mkdir -p $WP_CORE_DIR
+
+	if [[ $WP_VERSION == 'nightly' || $WP_VERSION == 'trunk' ]]; then
+		mkdir -p $TMPDIR/wordpress-nightly
+		download https://wordpress.org/nightly-builds/wordpress-latest.zip  $TMPDIR/wordpress-nightly/wordpress-nightly.zip
+		unzip -q $TMPDIR/wordpress-nightly/wordpress-nightly.zip -d $TMPDIR/wordpress-nightly/
+		mv $TMPDIR/wordpress-nightly/wordpress/* $WP_CORE_DIR
+	else
+		if [ $WP_VERSION == 'latest' ]; then
+			local ARCHIVE_NAME='latest'
+		elif [[ $WP_VERSION =~ [0-9]+\.[0-9]+ ]]; then
+			# https serves multiple offers, whereas http serves single.
+			download https://api.wordpress.org/core/version-check/1.7/ $TMPDIR/wp-latest.json
+			if [[ $WP_VERSION =~ [0-9]+\.[0-9]+\.[0] ]]; then
+				# version x.x.0 means the first release of the major version, so strip off the .0 and download version x.x
+				LATEST_VERSION=${WP_VERSION%??}
+			else
+				# otherwise, use the exact version
+				LATEST_VERSION=$WP_VERSION
+			fi
+			local ARCHIVE_NAME="wordpress-$LATEST_VERSION"
+		else
+			local ARCHIVE_NAME="wordpress-$WP_VERSION"
+		fi
+		download https://wordpress.org/${ARCHIVE_NAME}.tar.gz  $TMPDIR/wordpress.tar.gz
+		tar --strip-components=1 -zxmf $TMPDIR/wordpress.tar.gz -C $WP_CORE_DIR
+	fi
+
+	download https://raw.github.com/markoheijnen/wp-mysqli/master/db.php $WP_CORE_DIR/wp-content/db.php
+}
+
+install_test_suite() {
+	# portable in-place argument for both GNU sed and Mac OSX sed
+	if [[ $(uname -s) == 'Darwin' ]]; then
+		local ioption='-i .bak'
+	else
+		local ioption='-i'
+	fi
+
+	# set up testing suite if it doesn't yet exist
+	if [ ! -d $WP_TESTS_DIR ]; then
+		# set up testing suite
+		mkdir -p $WP_TESTS_DIR
+		svn co --quiet https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/includes/ $WP_TESTS_DIR/includes
+		svn co --quiet https://develop.svn.wordpress.org/${WP_TESTS_TAG}/tests/phpunit/data/ $WP_TESTS_DIR/data
+	fi
+
+	if [ ! -f wp-tests-config.php ]; then
+		download https://develop.svn.wordpress.org/${WP_TESTS_TAG}/wp-tests-config-sample.php "$WP_TESTS_DIR"/wp-tests-config.php
+		# remove all forward slashes in the end
+		WP_CORE_DIR=$(echo $WP_CORE_DIR | sed "s:/\+$::")
+		sed $ioption "s:dirname( __FILE__ ) . '/src/':'$WP_CORE_DIR/':" "$WP_TESTS_DIR"/wp-tests-config.php
+		sed $ioption "s/youremptytestdbnamehere/$DB_NAME/" "$WP_TESTS_DIR"/wp-tests-config.php
+		sed $ioption "s/yourusernamehere/$DB_USER/" "$WP_TESTS_DIR"/wp-tests-config.php
+		sed $ioption "s/yourpasswordhere/$DB_PASS/" "$WP_TESTS_DIR"/wp-tests-config.php
+		sed $ioption "s|localhost|${DB_HOST}|" "$WP_TESTS_DIR"/wp-tests-config.php
+	fi
+
+}
+
+install_db() {
+
+	if [ ${SKIP_DB_CREATE} = "true" ]; then
+		return 0
+	fi
+
+	# parse DB_HOST for port or socket references
+	local PARTS=(${DB_HOST//\:/ })
+	local DB_HOSTNAME=${PARTS[0]};
+	local DB_SOCK_OR_PORT=${PARTS[1]};
+	local EXTRA=""
+
+	if ! [ -z $DB_HOSTNAME ] ; then
+		if [ $(echo $DB_SOCK_OR_PORT | grep -e '^[0-9]\{1,\}$') ]; then
+			EXTRA=" --host=$DB_HOSTNAME --port=$DB_SOCK_OR_PORT --protocol=tcp"
+		elif ! [ -z $DB_SOCK_OR_PORT ] ; then
+			EXTRA=" --socket=$DB_SOCK_OR_PORT"
+		elif ! [ -z $DB_HOSTNAME ] ; then
+			EXTRA=" --host=$DB_HOSTNAME --protocol=tcp"
+		fi
+	fi
+
+	# create database
+	mysqladmin create $DB_NAME --user="$DB_USER" --password="$DB_PASS"$EXTRA
+}
+
+install_wp
+install_test_suite
+install_db
\ No newline at end of file
diff --git a/options.php b/options.php
index 6288a4e..bce56c6 100644
--- a/options.php
+++ b/options.php
@@ -253,18 +253,42 @@ public function page_init() {
    * @param array $input Contains all settings fields as array keys
    */
   public function sanitize( $input ) {
-    foreach( ['scss_dir', 'css_dir'] as $dir ){
+    $new_input = array();
+
+    // Sanitize directory paths
+    foreach( ['scss_dir', 'css_dir', 'cache_dir'] as $dir ){
       if( !empty( $input[$dir] ) ) {
-        $input[$dir] = sanitize_text_field( $input[$dir] );
+        $new_input[$dir] = sanitize_text_field( $input[$dir] );
 
         // Add a trailing slash if not already present
-        if(substr($input[$dir], -1) != '/'){
-          $input[$dir] .= '/';
+        if(substr($new_input[$dir], -1) != '/'){
+          $new_input[$dir] .= '/';
         }
       }
     }
 
-    return $input;
+    // Sanitize other text fields
+    if( !empty( $input['base_compiling_folder'] ) ) {
+      $new_input['base_compiling_folder'] = sanitize_text_field( $input['base_compiling_folder'] );
+    }
+
+    if( !empty( $input['compiling_options'] ) ) {
+      $new_input['compiling_options'] = sanitize_text_field( $input['compiling_options'] );
+    }
+
+    if( !empty( $input['sourcemap_options'] ) ) {
+      $new_input['sourcemap_options'] = sanitize_text_field( $input['sourcemap_options'] );
+    }
+
+    if( !empty( $input['errors'] ) ) {
+      $new_input['errors'] = sanitize_text_field( $input['errors'] );
+    }
+
+    // Sanitize checkbox fields
+    $new_input['enqueue'] = !empty( $input['enqueue'] ) ? '1' : '0';
+    $new_input['always_recompile'] = !empty( $input['always_recompile'] ) ? '1' : '0';
+
+    return $new_input;
   }
 
   /**
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..45084e7
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,18 @@
+<?xml version="1.0"?>
+<phpunit
+    bootstrap="tests/bootstrap.php"
+    backupGlobals="false"
+    colors="true"
+    convertErrorsToExceptions="true"
+    convertNoticesToExceptions="true"
+    convertWarningsToExceptions="true"
+    >
+    <testsuites>
+        <testsuite name="WP-SCSS Plugin Tests">
+            <directory>./tests/</directory>
+        </testsuite>
+    </testsuites>
+    <logging>
+        <log type="coverage-clover" target="build/logs/clover.xml"/>
+    </logging>
+</phpunit>
\ No newline at end of file
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
new file mode 100644
index 0000000..20536c7
--- /dev/null
+++ b/tests/bootstrap.php
@@ -0,0 +1,30 @@
+<?php
+/**
+ * PHPUnit bootstrap file for WP-SCSS plugin tests
+ */
+
+// WordPress test environment setup
+$_tests_dir = getenv( 'WP_TESTS_DIR' );
+
+if ( ! $_tests_dir ) {
+    $_tests_dir = rtrim( sys_get_temp_dir(), '/\\' ) . '/wordpress-tests-lib';
+}
+
+if ( ! file_exists( $_tests_dir . '/includes/functions.php' ) ) {
+    echo "Could not find $_tests_dir/includes/functions.php, have you run bin/install-wp-tests.sh ?" . PHP_EOL; // phpcs:ignore WordPress.Security.EscapeOutput.OutputNotEscaped
+    exit( 1 );
+}
+
+// Give access to tests_add_filter() function.
+require_once $_tests_dir . '/includes/functions.php';
+
+/**
+ * Manually load the plugin being tested.
+ */
+function _manually_load_plugin() {
+    require dirname( dirname( __FILE__ ) ) . '/wp-scss.php';
+}
+tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );
+
+// Start up the WP testing environment.
+require $_tests_dir . '/includes/bootstrap.php';
\ No newline at end of file
diff --git a/tests/test-settings.php b/tests/test-settings.php
new file mode 100644
index 0000000..c93ada0
--- /dev/null
+++ b/tests/test-settings.php
@@ -0,0 +1,190 @@
+<?php
+/**
+ * Tests for WP_Scss_Settings class
+ */
+
+class Test_WP_SCSS_Settings extends WP_UnitTestCase {
+
+    private $settings_instance;
+
+    public function setUp(): void {
+        parent::setUp();
+        
+        // Include the options file to load the class
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        
+        $this->settings_instance = new Wp_Scss_Settings();
+    }
+
+    public function tearDown(): void {
+        parent::tearDown();
+        
+        // Clean up options
+        delete_option( 'wpscss_options' );
+    }
+
+    /**
+     * Test that the sanitize method preserves all form fields
+     * This tests the bug fix for settings not being saved
+     */
+    public function test_sanitize_preserves_all_fields() {
+        $input = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'compressed',
+            'sourcemap_options' => 'SOURCE_MAP_NONE',
+            'errors' => 'show',
+            'enqueue' => '1',
+            'always_recompile' => '1'
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        // Test that all fields are preserved
+        $this->assertEquals( 'Current Theme', $result['base_compiling_folder'] );
+        $this->assertEquals( '/scss/', $result['scss_dir'] );
+        $this->assertEquals( '/css/', $result['css_dir'] );
+        $this->assertEquals( '/cache/', $result['cache_dir'] );
+        $this->assertEquals( 'compressed', $result['compiling_options'] );
+        $this->assertEquals( 'SOURCE_MAP_NONE', $result['sourcemap_options'] );
+        $this->assertEquals( 'show', $result['errors'] );
+        $this->assertEquals( '1', $result['enqueue'] );
+        $this->assertEquals( '1', $result['always_recompile'] );
+    }
+
+    /**
+     * Test directory path sanitization with trailing slash addition
+     */
+    public function test_sanitize_adds_trailing_slashes() {
+        $input = array(
+            'scss_dir' => '/scss',
+            'css_dir' => '/css',
+            'cache_dir' => '/cache'
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        $this->assertEquals( '/scss/', $result['scss_dir'] );
+        $this->assertEquals( '/css/', $result['css_dir'] );
+        $this->assertEquals( '/cache/', $result['cache_dir'] );
+    }
+
+    /**
+     * Test that directory paths already with trailing slashes are preserved
+     */
+    public function test_sanitize_preserves_existing_trailing_slashes() {
+        $input = array(
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/'
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        $this->assertEquals( '/scss/', $result['scss_dir'] );
+        $this->assertEquals( '/css/', $result['css_dir'] );
+        $this->assertEquals( '/cache/', $result['cache_dir'] );
+    }
+
+    /**
+     * Test checkbox field handling
+     */
+    public function test_sanitize_checkbox_fields() {
+        // Test checkbox checked
+        $input_checked = array(
+            'enqueue' => '1',
+            'always_recompile' => '1'
+        );
+
+        $result = $this->settings_instance->sanitize( $input_checked );
+        $this->assertEquals( '1', $result['enqueue'] );
+        $this->assertEquals( '1', $result['always_recompile'] );
+
+        // Test checkbox unchecked (empty)
+        $input_unchecked = array();
+
+        $result = $this->settings_instance->sanitize( $input_unchecked );
+        $this->assertEquals( '0', $result['enqueue'] );
+        $this->assertEquals( '0', $result['always_recompile'] );
+    }
+
+    /**
+     * Test handling of empty/missing fields
+     */
+    public function test_sanitize_handles_empty_fields() {
+        $input = array(
+            'base_compiling_folder' => '',
+            'scss_dir' => '',
+            'css_dir' => '/css/',
+            'compiling_options' => '',
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        // Empty fields should not be set in result
+        $this->assertArrayNotHasKey( 'base_compiling_folder', $result );
+        $this->assertArrayNotHasKey( 'scss_dir', $result );
+        $this->assertArrayNotHasKey( 'compiling_options', $result );
+        
+        // Non-empty fields should be preserved
+        $this->assertEquals( '/css/', $result['css_dir'] );
+        
+        // Checkboxes should default to '0'
+        $this->assertEquals( '0', $result['enqueue'] );
+        $this->assertEquals( '0', $result['always_recompile'] );
+    }
+
+    /**
+     * Test text field sanitization
+     */
+    public function test_sanitize_text_fields() {
+        $input = array(
+            'base_compiling_folder' => '<script>alert("xss")</script>Current Theme',
+            'compiling_options' => 'compressed<script>',
+            'sourcemap_options' => 'SOURCE_MAP_NONE',
+            'errors' => 'show'
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        // Should strip harmful content
+        $this->assertEquals( 'Current Theme', $result['base_compiling_folder'] );
+        $this->assertEquals( 'compressed', $result['compiling_options'] );
+        $this->assertEquals( 'SOURCE_MAP_NONE', $result['sourcemap_options'] );
+        $this->assertEquals( 'show', $result['errors'] );
+    }
+
+    /**
+     * Test regression: the original bug where only scss_dir and css_dir were preserved
+     * This ensures our fix works correctly
+     */
+    public function test_bug_fix_all_settings_preserved() {
+        // Simulate the exact scenario from the bug report
+        $input = array(
+            'base_compiling_folder' => 'Current Theme',  // This was getting lost
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'expanded',           // This was getting lost
+            'sourcemap_options' => 'SOURCE_MAP_FILE',    // This was getting lost
+            'errors' => 'show-logged-in',                // This was getting lost
+            'enqueue' => '1',                           // This was getting lost
+            'always_recompile' => '0'                   // This was getting lost
+        );
+
+        $result = $this->settings_instance->sanitize( $input );
+
+        // All 9 fields should be present in the result
+        $this->assertCount( 9, $result );
+        
+        // Specifically test the fields that were getting lost
+        $this->assertEquals( 'Current Theme', $result['base_compiling_folder'] );
+        $this->assertEquals( 'expanded', $result['compiling_options'] );
+        $this->assertEquals( 'SOURCE_MAP_FILE', $result['sourcemap_options'] );
+        $this->assertEquals( 'show-logged-in', $result['errors'] );
+        $this->assertEquals( '1', $result['enqueue'] );
+        $this->assertEquals( '0', $result['always_recompile'] );
+    }
+}
\ No newline at end of file
diff --git a/tests/test-wp-scss-integration.php b/tests/test-wp-scss-integration.php
new file mode 100644
index 0000000..687cd01
--- /dev/null
+++ b/tests/test-wp-scss-integration.php
@@ -0,0 +1,219 @@
+<?php
+/**
+ * Integration tests for WP-SCSS plugin settings persistence
+ */
+
+class Test_WP_SCSS_Integration extends WP_UnitTestCase {
+
+    public function setUp(): void {
+        parent::setUp();
+        
+        // Clean slate for each test
+        delete_option( 'wpscss_options' );
+    }
+
+    public function tearDown(): void {
+        parent::tearDown();
+        
+        // Clean up
+        delete_option( 'wpscss_options' );
+    }
+
+    /**
+     * Test complete settings save and retrieve cycle
+     * This simulates the exact user workflow from the bug report
+     */
+    public function test_settings_persistence_workflow() {
+        // Simulate form submission data
+        $form_data = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'expanded',
+            'sourcemap_options' => 'SOURCE_MAP_FILE',
+            'errors' => 'show-logged-in',
+            'enqueue' => '1',
+            'always_recompile' => '0'
+        );
+
+        // Include and instantiate the settings class
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        $settings = new Wp_Scss_Settings();
+
+        // Sanitize the input (this is what WordPress does during save)
+        $sanitized_data = $settings->sanitize( $form_data );
+
+        // Save to database (WordPress handles this automatically)
+        update_option( 'wpscss_options', $sanitized_data );
+
+        // Retrieve and verify
+        $saved_options = get_option( 'wpscss_options' );
+
+        $this->assertIsArray( $saved_options );
+        $this->assertEquals( 'Current Theme', $saved_options['base_compiling_folder'] );
+        $this->assertEquals( '/scss/', $saved_options['scss_dir'] );
+        $this->assertEquals( '/css/', $saved_options['css_dir'] );
+        $this->assertEquals( '/cache/', $saved_options['cache_dir'] );
+        $this->assertEquals( 'expanded', $saved_options['compiling_options'] );
+        $this->assertEquals( 'SOURCE_MAP_FILE', $saved_options['sourcemap_options'] );
+        $this->assertEquals( 'show-logged-in', $saved_options['errors'] );
+        $this->assertEquals( '1', $saved_options['enqueue'] );
+        $this->assertEquals( '0', $saved_options['always_recompile'] );
+    }
+
+    /**
+     * Test the specific bug scenario: changing base location
+     */
+    public function test_base_location_change_persistence() {
+        // Initial state: base location is "Uploads Directory"
+        $initial_options = array(
+            'base_compiling_folder' => 'Uploads Directory',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'compiling_options' => 'compressed'
+        );
+        update_option( 'wpscss_options', $initial_options );
+
+        // User changes base location to "Current Theme"
+        $updated_form_data = array(
+            'base_compiling_folder' => 'Current Theme',  // Changed
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'compressed',
+            'sourcemap_options' => 'SOURCE_MAP_NONE',
+            'errors' => 'show',
+            'enqueue' => '0',
+            'always_recompile' => '0'
+        );
+
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        $settings = new Wp_Scss_Settings();
+
+        // Process the update
+        $sanitized_data = $settings->sanitize( $updated_form_data );
+        update_option( 'wpscss_options', $sanitized_data );
+
+        // Verify the change persisted
+        $saved_options = get_option( 'wpscss_options' );
+        $this->assertEquals( 'Current Theme', $saved_options['base_compiling_folder'] );
+        
+        // Verify other settings weren't lost
+        $this->assertEquals( '/scss/', $saved_options['scss_dir'] );
+        $this->assertEquals( '/css/', $saved_options['css_dir'] );
+        $this->assertEquals( 'compressed', $saved_options['compiling_options'] );
+    }
+
+    /**
+     * Test development mode setting persistence
+     */
+    public function test_development_mode_persistence() {
+        $form_data = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'expanded',  // Changed to expanded (development mode)
+            'sourcemap_options' => 'SOURCE_MAP_INLINE',
+            'errors' => 'show',
+            'enqueue' => '1',
+            'always_recompile' => '1'  // Development mode enabled
+        );
+
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        $settings = new Wp_Scss_Settings();
+
+        $sanitized_data = $settings->sanitize( $form_data );
+        update_option( 'wpscss_options', $sanitized_data );
+
+        $saved_options = get_option( 'wpscss_options' );
+        
+        // Verify development settings are saved
+        $this->assertEquals( 'expanded', $saved_options['compiling_options'] );
+        $this->assertEquals( 'SOURCE_MAP_INLINE', $saved_options['sourcemap_options'] );
+        $this->assertEquals( '1', $saved_options['always_recompile'] );
+    }
+
+    /**
+     * Test checkbox handling in real WordPress context
+     */
+    public function test_checkbox_form_behavior() {
+        // When checkboxes are checked, they submit their value
+        $form_data_checked = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'enqueue' => '1',           // Checkbox checked
+            'always_recompile' => '1'   // Checkbox checked
+        );
+
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        $settings = new Wp_Scss_Settings();
+
+        $sanitized_data = $settings->sanitize( $form_data_checked );
+        update_option( 'wpscss_options', $sanitized_data );
+
+        $saved_options = get_option( 'wpscss_options' );
+        $this->assertEquals( '1', $saved_options['enqueue'] );
+        $this->assertEquals( '1', $saved_options['always_recompile'] );
+
+        // When checkboxes are unchecked, they don't submit at all
+        $form_data_unchecked = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            // No 'enqueue' or 'always_recompile' keys = unchecked
+        );
+
+        $sanitized_data = $settings->sanitize( $form_data_unchecked );
+        update_option( 'wpscss_options', $sanitized_data );
+
+        $saved_options = get_option( 'wpscss_options' );
+        $this->assertEquals( '0', $saved_options['enqueue'] );
+        $this->assertEquals( '0', $saved_options['always_recompile'] );
+    }
+
+    /**
+     * Test that the bug is actually fixed by simulating the old broken behavior
+     */
+    public function test_old_sanitize_method_would_fail() {
+        $form_data = array(
+            'base_compiling_folder' => 'Current Theme',
+            'scss_dir' => '/scss/',
+            'css_dir' => '/css/',
+            'cache_dir' => '/cache/',
+            'compiling_options' => 'expanded',
+            'sourcemap_options' => 'SOURCE_MAP_FILE',
+            'errors' => 'show-logged-in',
+            'enqueue' => '1',
+            'always_recompile' => '0'
+        );
+
+        // Simulate the old broken sanitize method
+        $old_broken_result = array();
+        foreach( ['scss_dir', 'css_dir'] as $dir ){
+            if( !empty( $form_data[$dir] ) ) {
+                $old_broken_result[$dir] = sanitize_text_field( $form_data[$dir] );
+                if(substr($old_broken_result[$dir], -1) != '/'){
+                    $old_broken_result[$dir] .= '/';
+                }
+            }
+        }
+        // Old method only returned scss_dir and css_dir, losing everything else
+
+        $this->assertCount( 2, $old_broken_result );  // Old method only saved 2 fields
+        $this->assertArrayNotHasKey( 'base_compiling_folder', $old_broken_result );
+        $this->assertArrayNotHasKey( 'compiling_options', $old_broken_result );
+
+        // Now test our fixed method
+        require_once dirname( dirname( __FILE__ ) ) . '/options.php';
+        $settings = new Wp_Scss_Settings();
+        $fixed_result = $settings->sanitize( $form_data );
+
+        $this->assertCount( 9, $fixed_result );  // Fixed method saves all fields
+        $this->assertArrayHasKey( 'base_compiling_folder', $fixed_result );
+        $this->assertArrayHasKey( 'compiling_options', $fixed_result );
+        $this->assertEquals( 'Current Theme', $fixed_result['base_compiling_folder'] );
+    }
+}
\ No newline at end of file