Index: modules/simpletest/drupal_web_test_case.php
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/drupal_web_test_case.php,v
retrieving revision 1.55
diff -u -r1.55 drupal_web_test_case.php
--- modules/simpletest/drupal_web_test_case.php	5 Nov 2008 17:06:18 -0000	1.55
+++ modules/simpletest/drupal_web_test_case.php	8 Nov 2008 09:04:44 -0000
@@ -684,19 +684,75 @@
   function setUp() {
     global $db_prefix;
 
+    $modules = func_get_args();
+    if (!variable_get('simpletest_install_cached', FALSE)) {
+      // Delete temporary files directory and reset files directory path.
+      if (is_dir(file_directory_path() . '/simpletest_base')) {
+        simpletest_clean_temporary_directory(file_directory_path() . '/simpletest_base');
+      }
+
+      // Clear previous cache.
+      $tables = db_find_tables(Database::getActiveConnection()->prefixTables('{simpletest_base}') . '%');
+      $ret = array();
+      foreach ($tables as $table) {
+        db_drop_table($ret, $table);
+      }
+
+      // Create base installation to be re-used.
+      $this->installDrupal('_base');
+
+      // Revert variables in preparation for testing instance installation.
+      variable_set('file_directory_path', $this->original_file_directory);
+      $db_prefix = $this->db_prefix_original;
+
+      $simpletest_install_prefix = mt_rand(1000, 1000000);
+      variable_set('simpletest_install_cached', TRUE);
+      variable_set('simpletest_install_prefix', $simpletest_install_prefix);
+
+      $this->installDrupal($simpletest_install_prefix, $modules);
+      return;
+    }
+
+    $this->installDrupal(variable_get('simpletest_install_prefix', ''), $modules, TRUE);
+  }
+
+  private function installDrupal($prefix, $modules = array(), $from_cache = FALSE) {
+    global $db_prefix;
+
     // Store necessary current values before switching to prefixed database.
     $this->db_prefix_original = $db_prefix;
     $clean_url_original = variable_get('clean_url', 0);
 
     // Generate temporary prefixed database to ensure that tests have a clean starting point.
-    $db_prefix = Database::getActiveConnection()->prefixTables('{simpletest' . mt_rand(1000, 1000000) . '}');
+    $db_prefix = Database::getActiveConnection()->prefixTables('{simpletest' . $prefix . '}');
 
-    include_once DRUPAL_ROOT . '/includes/install.inc';
-    drupal_install_system();
+    require_once DRUPAL_ROOT . '/includes/install.inc';
+    if ($from_cache) {
+      // TODO Copy files?.
+      // Copy tables from cache.
+      $db_prefix = Database::getActiveConnection()->prefixTables($this->db_prefix_original);
+      $tables = db_find_tables(Database::getActiveConnection()->prefixTables('{simpletest_base}') . '%');
+      $db_prefix = Database::getActiveConnection()->prefixTables('{simpletest' . $prefix . '}');
+      foreach ($tables as $table) {
+        $base_name = str_replace('simpletest_base', '', $table);
+        // Garbage to deal with uid = 0...bad.
+        if ($base_name == 'users') {
+          db_query('INSERT INTO {users} SELECT * FROM ' . $table . ' WHERE uid = 0');
+          db_query('UPDATE {users} SET uid = uid - 1');
+          db_query('INSERT INTO {users} SELECT * FROM ' . $table . ' WHERE uid > 0');
+          continue;
+        }
+        db_query('INSERT INTO {' . $base_name . '} SELECT * FROM ' . $table);
+      }
+    }
+    else {
+      drupal_install_system();
+    }
 
     // Add the specified modules to the list of modules in the default profile.
-    $args = func_get_args();
-    $modules = array_unique(array_merge(drupal_get_profile_modules('default', 'en'), $args));
+    if (!$from_cache) {
+      $modules = array_unique(array_merge(drupal_get_profile_modules('default', 'en'), $modules));
+    }
     drupal_install_modules($modules);
 
     // Because the schema is static cached, we need to flush
@@ -706,8 +762,10 @@
     drupal_get_schema(NULL, TRUE);
 
     // Run default profile tasks.
-    $task = 'profile';
-    default_profile_tasks($task, '');
+    if (!$from_cache) {
+      $task = 'profile';
+      default_profile_tasks($task, '');
+    }
 
     // Rebuild caches.
     menu_rebuild();
@@ -761,7 +819,7 @@
       $schema = drupal_get_schema(NULL, TRUE);
       $ret = array();
       foreach ($schema as $name => $table) {
-        db_drop_table($ret, $name);
+        db_query('TRUNCATE {' . $name . '}');
       }
 
       // Return the database prefix to the original.
Index: modules/simpletest/simpletest.module
===================================================================
RCS file: /cvs/drupal/drupal/modules/simpletest/simpletest.module,v
retrieving revision 1.26
diff -u -r1.26 simpletest.module
--- modules/simpletest/simpletest.module	1 Nov 2008 21:21:35 -0000	1.26
+++ modules/simpletest/simpletest.module	8 Nov 2008 09:04:44 -0000
@@ -342,6 +342,10 @@
  *   drupal being the default.
  */
 function simpletest_run_tests($test_list, $reporter = 'drupal') {
+  // Force SimpleTest to create new cache during first test run.
+  variable_del('simpletest_install_cached');
+  variable_del('simpletest_install_prefix');
+
   global $db_prefix, $db_prefix_original;
   cache_clear_all();
   $test_id = db_insert('simpletest_test_id')->useDefaults(array('test_id'))->execute();
@@ -521,7 +525,7 @@
   foreach (array_diff_key($tables, $schema) as $table) {
     // Strip $db_prefix and skip tables without digits following "simpletest",
     // e.g. {simpletest_tets_id}.
-    if (preg_match('/simpletest\d+.*/', $table, $matches)) {
+    if (preg_match('/simpletest\d+.*/', $table, $matches) || preg_match('/simpletest_base.*/', $table, $matches)) {
       db_drop_table($ret, $matches[0]);
     }
   }