.wp-env.json schema: Fix schema and add unit tests

schemas/json/wp-env.json

@@ -82,6 +82,7 @@
 			"$ref": "#/definitions/wpEnvProperties"
 		},
 		{
+			"type": "object",
 			"properties": {
 				"$schema": {
 					"type": "string"
@@ -91,10 +92,10 @@
 					"type": "object",
 					"patternProperties": {
 						"[a-zA-Z]": {
-							"type": "object",
 							"allOf": [
 								{ "$ref": "#/definitions/wpEnvProperties" },
 								{
+									"type": "object",
 									"propertyNames": {
 										"$ref": "#/definitions/wpEnvPropertyNames"
 									}
@@ -107,6 +108,7 @@
 			}
 		},
 		{
+			"type": "object",
 			"propertyNames": {
 				"anyOf": [
 					{

test/integration/wp-env-schema.test.js

@@ -0,0 +1,38 @@
+/**
+ * External dependencies
+ */
+import Ajv from 'ajv';
+
+/**
+ * Internal dependencies
+ */
+import wpEnvSchema from '../../schemas/json/wp-env.json';
+import wpEnvJsonFile from '../../.wp-env.json';
+
+describe( '.wp-env.json schema', () => {
+	const ajv = new Ajv( {
+		allowMatchingProperties: true,
+	} );
+
+	test( 'strictly adheres to the draft-07 meta schema', () => {
+		// Use ajv.compile instead of ajv.validateSchema to validate the schema
+		// because validateSchema only checks syntax, whereas, compile checks
+		// if the schema is semantically correct with strict mode.
+		// See https://github.com/ajv-validator/ajv/issues/1434#issuecomment-822982571
+		const result = ajv.compile( wpEnvSchema );
+
+		expect( result.errors ).toBe( null );
+	} );
+
+	test( 'validates schema for .wp-env.json', () => {
+		// We want to validate the .wp-env.json file using the local schema.
+		const { $schema, ...metadata } = wpEnvJsonFile;
+
+		// we expect the $schema property to be present in the .wp-env.json file
+		expect( $schema ).toBeTruthy();
+
+		const result = ajv.validate( wpEnvSchema, metadata ) || ajv.errors;
+
+		expect( result ).toBe( true );
+	} );
+} );