Add WP_ENV_MULTISITE environment variable.

packages/env/README.md

@@ -701,6 +701,17 @@ You can tell `wp-env` to use a specific PHP version for compatibility and testin
 }
 ```
 
+### Specific if multisite is enabled
+
+You can tell `wp-env`  if the site should be multisite enabled. This can also be set via the environment variable `WP_ENV_MULTISITE`.
+
+```json
+{
+	"multsite": true,
+	"plugins": [ "." ]
+}
+```
+
 ### Node Lifecycle Script
 
 This is useful for performing some actions after setting up the environment, such as bootstrapping an E2E test environment.

packages/env/lib/config/get-config-from-environment-vars.js

@@ -23,6 +23,7 @@ const { checkPort, checkVersion, checkString } = require( './validate-config' );
  * @property {?number}                  phpmyadminPort   An override for the development environment's phpMyAdmin port.
  * @property {?WPSource}                coreSource       An override for all environment's coreSource.
  * @property {?string}                  phpVersion       An override for all environment's PHP version.
+ * @property {?bool}                  multisite       An override for if environmen should be multisite.
  * @property {?Object.<string, string>} lifecycleScripts An override for various lifecycle scripts.
  */
 
@@ -68,6 +69,10 @@ module.exports = function getConfigFromEnvironmentVars( cacheDirectoryPath ) {
 		environmentConfig.phpVersion = process.env.WP_ENV_PHP_VERSION;
 	}
 
+	if ( process.env.WP_ENV_MULTISITE ) {
+		environmentConfig.multisite = !!process.env.WP_ENV_MULTISITE;
+	}
+
 	return environmentConfig;
 };