diff --git a/README.md b/README.md
index 44bae60c..5e80e739 100644
--- a/README.md
+++ b/README.md
@@ -356,7 +356,6 @@ The following tests are not yet implemented and therefore missing:
 
 **Recommended Tests**
 
-- Recommended Test 6.2.20
 - Recommended Test 6.2.24
 - Recommended Test 6.2.26
 - Recommended Test 6.2.31
@@ -502,6 +501,7 @@ export const recommendedTest_6_2_16: DocumentTest
 export const recommendedTest_6_2_17: DocumentTest
 export const recommendedTest_6_2_18: DocumentTest
 export const recommendedTest_6_2_19: DocumentTest
+export const recommendedTest_6_2_20: DocumentTest
 export const recommendedTest_6_2_21: DocumentTest
 export const recommendedTest_6_2_22: DocumentTest
 export const recommendedTest_6_2_23: DocumentTest
diff --git a/csaf_2_1/csafAjv.js b/csaf_2_1/csafAjv.js
index 429f5d87..6f7df1ec 100644
--- a/csaf_2_1/csafAjv.js
+++ b/csaf_2_1/csafAjv.js
@@ -1,8 +1,8 @@
 import addFormats from 'ajv-formats'
 import { Ajv2020 } from 'ajv/dist/2020.js'
-import cvss_v2_0 from '../schemas/cvss-v2.0.js'
-import cvss_v3_0 from '../schemas/cvss-v3.0.js'
-import cvss_v3_1 from '../schemas/cvss-v3.1.js'
+import cvss_v2_0 from './csafAjv/cvss-v2.0.js'
+import cvss_v3_0 from './csafAjv/cvss-v3.0.js'
+import cvss_v3_1 from './csafAjv/cvss-v3.1.js'
 import cvss_v4_0_0 from './csafAjv/cvss-v4.0.0.js'
 import extension_content from './csafAjv/extension-content.js'
 import content_schema from './csafAjv/content_schema.js'
@@ -11,6 +11,7 @@ import cvss_meta from './csafAjv/cvss_meta.js'
 import meta_format_assertion from './csafAjv/meta-format-assertion.js'
 import draft_07_schema from './csafAjv/draft-07-schema.js'
 import selectionList_2_0_0Schema from './csafAjv/SelectionList_2_0_0.schema.js'
+import { registerExtensionSchemas } from './csafAjv/extensionSchemas/index.js'
 
 import { validateTimestamp } from './dateHelper.js'
 
@@ -45,6 +46,7 @@ csafAjv.addSchema(
   selectionList_2_0_0Schema,
   'https://certcc.github.io/SSVC/data/schema/v2/SelectionList_2_0_0.schema.json'
 )
+registerExtensionSchemas(csafAjv)
 
 csafAjv.addFormat('date-time', {
   type: 'string',
diff --git a/csaf_2_1/csafAjv/cvss-v2.0.js b/csaf_2_1/csafAjv/cvss-v2.0.js
index cf791137..4833f1ce 100644
--- a/csaf_2_1/csafAjv/cvss-v2.0.js
+++ b/csaf_2_1/csafAjv/cvss-v2.0.js
@@ -24,6 +24,7 @@ export default {
   title: 'JSON Schema for Common Vulnerability Scoring System version 2.0',
   $id: 'https://www.first.org/cvss/cvss-v2.0.json?20170531',
   type: 'object',
+  additionalProperties: false,
   $defs: {
     accessVectorType: {
       type: 'string',
diff --git a/csaf_2_1/csafAjv/cvss-v3.0.js b/csaf_2_1/csafAjv/cvss-v3.0.js
index c46f4ef2..f7c4e7cf 100644
--- a/csaf_2_1/csafAjv/cvss-v3.0.js
+++ b/csaf_2_1/csafAjv/cvss-v3.0.js
@@ -24,6 +24,7 @@ export default {
   title: 'JSON Schema for Common Vulnerability Scoring System version 3.0',
   $id: 'https://www.first.org/cvss/cvss-v3.0.json?20170531',
   type: 'object',
+  additionalProperties: false,
   $defs: {
     attackVectorType: {
       type: 'string',
diff --git a/csaf_2_1/csafAjv/cvss-v3.1.js b/csaf_2_1/csafAjv/cvss-v3.1.js
index d4b86cee..d6d0eefc 100644
--- a/csaf_2_1/csafAjv/cvss-v3.1.js
+++ b/csaf_2_1/csafAjv/cvss-v3.1.js
@@ -25,6 +25,7 @@ export default {
   title: 'JSON Schema for Common Vulnerability Scoring System version 3.1',
   $id: 'https://www.first.org/cvss/cvss-v3.1.json?20190610',
   type: 'object',
+  additionalProperties: false,
   $defs: {
     attackVectorType: {
       type: 'string',
diff --git a/csaf_2_1/csafAjv/extensionSchemas/documentation-11.js b/csaf_2_1/csafAjv/extensionSchemas/documentation-11.js
new file mode 100644
index 00000000..6f5d2538
--- /dev/null
+++ b/csaf_2_1/csafAjv/extensionSchemas/documentation-11.js
@@ -0,0 +1,54 @@
+// https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-11/documentation-11-content_1.0.0.json
+// Copied from ../../../csaf/csaf_2.1/test/extension/data/valid/documentation-11/documentation-11-content_1.0.0.json
+export default {
+  $schema:
+    'https://docs.oasis-open.org/csaf/csaf/v2.1/schema/extension-metaschema.json',
+  $id: 'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-11/documentation-11-content_1.0.0.json',
+  title: 'CSAF Extension: Documentation 11',
+  description:
+    'Representation of a valid extension used for documentation purposes.',
+  type: 'object',
+  required: ['$schema', 'category', 'critical', 'content'],
+  properties: {
+    $schema: {
+      title: 'CSAF Extension Schema',
+      description:
+        'Contains the URL of the CSAF Extension JSON schema which the JSON object promises to be valid for.',
+      type: 'string',
+      format: 'uri',
+      const:
+        'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-11/documentation-11-content_1.0.0.json',
+    },
+    category: {
+      title: 'Extension Category',
+      description: 'Holds the category of the extension content.',
+      type: 'string',
+      enum: ['essential', 'significant', 'supplementary'],
+    },
+    content: {
+      title: 'Content',
+      description: 'Contains the additional information in its properties.',
+      type: 'object',
+      minProperties: 1,
+      properties: {
+        documentation: {
+          title: 'Documentation content',
+          description:
+            'Contains a constant string to clarify that this is for documentation purposes only and not to be used in production.',
+          type: 'string',
+          const:
+            'This extension is for documentation and test purposed only. It is valid. It is not allowed to be used in a production CSAF.',
+        },
+      },
+      unevaluatedProperties: false,
+    },
+    critical: {
+      title: 'Critical',
+      description:
+        'Determines whether using the extension would fail a mandatory test.',
+      type: 'boolean',
+      const: false,
+    },
+  },
+  additionalProperties: false,
+}
diff --git a/csaf_2_1/csafAjv/extensionSchemas/documentation-12.js b/csaf_2_1/csafAjv/extensionSchemas/documentation-12.js
new file mode 100644
index 00000000..33f8eb88
--- /dev/null
+++ b/csaf_2_1/csafAjv/extensionSchemas/documentation-12.js
@@ -0,0 +1,68 @@
+// https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-12/documentation-12-content_1.0.0.json
+// Copied from ../../../csaf/csaf_2.1/test/extension/data/valid/documentation-12/documentation-12-content_1.0.0.json
+export default {
+  $schema:
+    'https://docs.oasis-open.org/csaf/csaf/v2.1/schema/extension-metaschema.json',
+  $id: 'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-12/documentation-12-content_1.0.0.json',
+  title: 'CSAF Extension: Documentation 12',
+  description:
+    'Representation of a valid extension used for documentation purposes.',
+  type: 'object',
+  required: ['$schema', 'category', 'critical', 'content'],
+  properties: {
+    $schema: {
+      title: 'CSAF Extension Schema',
+      description:
+        'Contains the URL of the CSAF Extension JSON schema which the JSON object promises to be valid for.',
+      type: 'string',
+      format: 'uri',
+      const:
+        'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-12/documentation-12-content_1.0.0.json',
+    },
+    category: {
+      title: 'Extension Category',
+      description: 'Holds the category of the extension content.',
+      type: 'string',
+      enum: ['essential', 'significant', 'supplementary'],
+    },
+    content: {
+      title: 'Content',
+      description: 'Contains the additional information in its properties.',
+      type: 'object',
+      minProperties: 1,
+      required: ['documentation'],
+      properties: {
+        documentation: {
+          title: 'Documentation content',
+          description:
+            'Contains a constant string to clarify that this is for documentation purposes only and not to be used in production.',
+          type: 'string',
+          const:
+            'This extension is for documentation and test purposed only. It is valid. It is not allowed to be used in a production CSAF.',
+        },
+        notes: {
+          title: 'Notes',
+          description:
+            'Contains a list of notes to convey a more complex structure.',
+          type: 'array',
+          minItems: 1,
+          items: {
+            title: 'Entry',
+            description: 'Contains a single entry.',
+            type: 'string',
+            minLength: 1,
+          },
+        },
+      },
+      unevaluatedProperties: false,
+    },
+    critical: {
+      title: 'Critical',
+      description:
+        'Determines whether using the extension would fail a mandatory test.',
+      type: 'boolean',
+      const: false,
+    },
+  },
+  additionalProperties: false,
+}
diff --git a/csaf_2_1/csafAjv/extensionSchemas/documentation-13.js b/csaf_2_1/csafAjv/extensionSchemas/documentation-13.js
new file mode 100644
index 00000000..343e23f8
--- /dev/null
+++ b/csaf_2_1/csafAjv/extensionSchemas/documentation-13.js
@@ -0,0 +1,129 @@
+// https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-13/documentation-13-content_1.0.0.json
+// Copied from ../../../csaf/csaf_2.1/test/extension/data/valid/documentation-13/documentation-13-content_1.0.0.json
+export default {
+  $schema:
+    'https://docs.oasis-open.org/csaf/csaf/v2.1/schema/extension-metaschema.json',
+  $id: 'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-13/documentation-13-content_1.0.0.json',
+  title: 'CSAF Extension: Documentation 13',
+  description:
+    'Representation of a valid extension for configurations used for documentation purposes.',
+  type: 'object',
+  $defs: {
+    configuration_id_t: {
+      title: 'Reference token for configuration instance',
+      description:
+        'Token required to identify a configuration so that it can be referred to from other parts in the document. There is no predefined or required format for the configuration_id as long as it uniquely identifies a configuration in the context of the current document.',
+      type: 'string',
+      minLength: 1,
+      examples: ['CSAFCID-0001', 'CSAFCID-0002'],
+    },
+    configuration_t: {
+      title: 'Configuration',
+      description:
+        'Contains the description of a configuration and assigns it a configuration id.',
+      type: 'object',
+      required: ['configuration_id', 'details'],
+      properties: {
+        configuration_id: { $ref: '#/$defs/configuration_id_t' },
+        details: {
+          title: 'Details of the Configuration',
+          description:
+            'Contains all details as human-readable description on how to identify the configuration.',
+          type: 'string',
+          minLength: 1,
+        },
+      },
+      additionalProperties: false,
+    },
+    relationship_t: {
+      title: 'Relationship',
+      description:
+        'Establishes a link between an existing full_product_name_t element and a configuration, allowing the document producer to define a combination that form a new full_product_name entry.',
+      type: 'object',
+      required: [
+        'configuration_reference',
+        'full_product_name',
+        'product_reference',
+      ],
+      properties: {
+        configuration_reference: {
+          title: 'Configuration Reference',
+          description:
+            'Holds a Configuration ID that refers to the Configuration element, which is referenced as the second element of the relationship.',
+          $ref: '#/$defs/configuration_id_t',
+        },
+        full_product_name: {
+          $ref: 'https://docs.oasis-open.org/csaf/csaf/v2.1/schema/csaf.json#/$defs/full_product_name_t',
+        },
+        product_reference: {
+          title: 'Product reference',
+          description:
+            'Holds a Product ID that refers to the Full Product Name element, which is referenced as the first element of the relationship.',
+          $ref: 'https://docs.oasis-open.org/csaf/csaf/v2.1/schema/csaf.json#/$defs/product_id_t',
+        },
+      },
+      additionalProperties: false,
+    },
+  },
+  required: ['$schema', 'category', 'critical', 'content'],
+  properties: {
+    $schema: {
+      title: 'CSAF Extension Schema',
+      description:
+        'Contains the URL of the CSAF Extension JSON schema which the JSON object promises to be valid for.',
+      type: 'string',
+      format: 'uri',
+      const:
+        'https://raw.githubusercontent.com/oasis-tcs/csaf/refs/heads/master/csaf_2.1/extension/data/valid/documentation-13/documentation-13-content_1.0.0.json',
+    },
+    category: {
+      title: 'Extension Category',
+      description: 'Holds the category of the extension content.',
+      type: 'string',
+      enum: ['essential', 'significant', 'supplementary'],
+    },
+    content: {
+      title: 'Content',
+      description: 'Contains the additional information in its properties.',
+      type: 'object',
+      minProperties: 1,
+      properties: {
+        configuration_tree: {
+          title: 'Configuration Tree',
+          description:
+            'Contains configurations and their bindings to products.',
+          type: 'object',
+          required: ['configurations', 'relationships'],
+          properties: {
+            configurations: {
+              title: 'List of Configurations',
+              description: 'Contains a list of configuration elements.',
+              type: 'array',
+              minItems: 1,
+              uniqueItems: true,
+              items: { $ref: '#/$defs/configuration_t' },
+            },
+            relationships: {
+              title: 'List of Relationships',
+              description:
+                'Contains a list of product-configuration combinations.',
+              type: 'array',
+              minItems: 1,
+              uniqueItems: true,
+              items: { $ref: '#/$defs/relationship_t' },
+            },
+          },
+        },
+      },
+      unevaluatedProperties: false,
+    },
+    critical: {
+      title: 'Critical',
+      description:
+        'Determines whether using the extension would fail a mandatory test.',
+      type: 'boolean',
+      const: true,
+    },
+  },
+  additionalProperties: false,
+}
diff --git a/csaf_2_1/csafAjv/extensionSchemas/index.js b/csaf_2_1/csafAjv/extensionSchemas/index.js
new file mode 100644
index 00000000..b6c4fa53
--- /dev/null
+++ b/csaf_2_1/csafAjv/extensionSchemas/index.js
@@ -0,0 +1,100 @@
+import documentation11 from './documentation-11.js'
+import documentation12 from './documentation-12.js'
+import documentation13 from './documentation-13.js'
+
+/**
+ * @typedef {object} ExtensionSchemaEntry
+ * @property {import('ajv').AnySchemaObject} schema
+ * @property {'official' | 'registered' | 'experimental'} class Extension
+ *   class as defined in spec section 2.4.1 ("Classes").
+ * @property {boolean} deprecated Whether this extension is on the OASIS CSAF
+ *   TC's list of deprecated extensions (spec section 2.4.2 "Lists"). Can
+ *   still be used, but support for it will be removed in the near future.
+ * @property {boolean} denyListed Whether this extension is on the OASIS CSAF
+ *   TC's list of deny-listed extensions (spec section 2.4.2 "Lists"). MUST
+ *   NOT be used.
+ */
+
+/**
+ * Allow list of CSAF Extension Schemas that this validator explicitly
+ * implements and supports at runtime.
+ *
+ * Per CSAF 2.1 spec chapter 8 ("Safety, Security, and Data Protection
+ * Considerations"), CSAF validators SHOULD NOT automatically retrieve JSON
+ * schemas from a URL declared in a CSAF document, and SHOULD instead keep a
+ * local copy of all schemas necessary to fulfill their tasks. Therefore, no
+ * schema referenced by an `x_extensions[].$schema` value is ever fetched over
+ * the network - only the schemas listed here are used to validate mandatory
+ * test 6.1.60.2.
+ *
+ * The `class`/`deprecated`/`denyListed` fields mirror the OASIS CSAF TC's
+ * lists described in spec section 2.4.2 ("Lists"). Those lists are not
+ * (yet) available as real, importable data in this repository - the entries
+ * below are currently limited to the OASIS documentation-11/12/13 test
+ * fixtures, which are themselves explicitly marked as "not allowed to be
+ * used in a production CSAF" and are therefore classified as `experimental`.
+ * The fields are still modeled explicitly so that real official/registered/
+ * deprecated/deny-listed extensions can be added later without having to
+ * change any consumer of this module.
+ *
+ * To add support for a new CSAF Extension Schema:
+ * 1. Add a new module next to this file that exports the schema (its `$id`
+ *    MUST match the `$schema` value that CSAF documents will declare).
+ * 2. Import it here and add an entry to `extensionSchemas` below with its
+ *    class and deprecated/deny-listed status.
+ *
+ * @type {ExtensionSchemaEntry[]}
+ */
+export const extensionSchemas = [
+  {
+    schema: documentation11,
+    class: 'experimental',
+    deprecated: false,
+    denyListed: false,
+  },
+  {
+    schema: documentation12,
+    class: 'experimental',
+    deprecated: false,
+    denyListed: false,
+  },
+  {
+    schema: documentation13,
+    class: 'experimental',
+    deprecated: false,
+    denyListed: false,
+  },
+]
+
+/**
+ * Registers all allow-listed extension schemas on the given Ajv instance so
+ * that `ajv.getSchema(schemaUrl)` resolves them without any network access.
+ *
+ * @param {import('ajv').default} ajv
+ */
+export function registerExtensionSchemas(ajv) {
+  for (const { schema } of extensionSchemas) {
+    ajv.addSchema(schema, schema.$id)
+  }
+}
+
+/**
+ * Classifies a CSAF Extension by its declared `$schema` URL, used to
+ * differentiate the warning raised for extensions that are not in the allow
+ * list above (see mandatoryTest_6_1_60_2).
+ *
+ * For allow-listed schemas, this returns the explicit class recorded in
+ * `extensionSchemas`. For any other schema, the class cannot be determined
+ * reliably: this validator does not have access to the OASIS CSAF TC's real
+ * lists of official/registered/deprecated/deny-listed extensions (spec
+ * section 2.4.2 "Lists"), which are not available as data in this
+ * repository, so guessing from the URL alone (e.g. by host name) would be
+ * misleading. `'unknown'` is returned in that case instead.
+ *
+ * @param {string} schemaUrl
+ * @returns {'official' | 'registered' | 'experimental' | 'unknown'}
+ */
+export function classifyExtensionSchema(schemaUrl) {
+  const entry = extensionSchemas.find((e) => e.schema.$id === schemaUrl)
+  return entry?.class ?? 'unknown'
+}
diff --git a/csaf_2_1/recommendedTests.js b/csaf_2_1/recommendedTests.js
index 714e3612..1a6f8837 100644
--- a/csaf_2_1/recommendedTests.js
+++ b/csaf_2_1/recommendedTests.js
@@ -25,6 +25,7 @@ export { recommendedTest_6_2_16 } from './recommendedTests/recommendedTest_6_2_1
 export { recommendedTest_6_2_17 } from './recommendedTests/recommendedTest_6_2_17.js'
 export { recommendedTest_6_2_18 } from './recommendedTests/recommendedTest_6_2_18.js'
 export { recommendedTest_6_2_19 } from './recommendedTests/recommendedTest_6_2_19.js'
+export { recommendedTest_6_2_20 } from './recommendedTests/recommendedTest_6_2_20.js'
 export { recommendedTest_6_2_21 } from './recommendedTests/recommendedTest_6_2_21.js'
 export { recommendedTest_6_2_22 } from './recommendedTests/recommendedTest_6_2_22.js'
 export { recommendedTest_6_2_23 } from './recommendedTests/recommendedTest_6_2_23.js'
diff --git a/csaf_2_1/recommendedTests/recommendedTest_6_2_20.js b/csaf_2_1/recommendedTests/recommendedTest_6_2_20.js
index b47b588a..bc2d0ccf 100644
--- a/csaf_2_1/recommendedTests/recommendedTest_6_2_20.js
+++ b/csaf_2_1/recommendedTests/recommendedTest_6_2_20.js
@@ -1,8 +1,70 @@
-import { optionalTest_6_2_20 } from '../../optionalTests.js'
+import schema from '../schemaTests/csaf_2_1_strict/schema.js'
+import csafAjv from '../csafAjv.js'
+import { walkPath } from '../../lib/walkPaths.js'
+import { classifyExtensionSchema } from '../csafAjv/extensionSchemas/index.js'
+
+const validateStrictSchema = csafAjv.compile(schema)
+
+const X_EXTENSIONS_PATHS = /** @type {const} */ ([
+  '/document/x_extensions[]',
+  '/product_tree/branches[*]/product/x_extensions[]',
+  '/product_tree/full_product_names[]/x_extensions[]',
+  '/product_tree/product_paths[]/full_product_name/x_extensions[]',
+  '/vulnerabilities[]/metrics[]/content/x_extensions[]',
+  '/vulnerabilities[]/x_extensions[]',
+  '/x_extensions[]',
+])
 
 /**
+ * This implements the recommended test 6.2.20 of the CSAF 2.1 standard.
+ *
  * @param {unknown} doc
  */
-export function recommendedTest_6_2_20(doc) {
-  return optionalTest_6_2_20(doc)
+export async function recommendedTest_6_2_20(doc) {
+  const ctx = {
+    warnings:
+      /** @type {Array<{ instancePath: string; message: string }>} */ ([]),
+  }
+
+  // Part 1: strict schema check – report any property not defined in the CSAF schema
+  if (!validateStrictSchema(doc)) {
+    const additionalPropertiesErrors =
+      validateStrictSchema.errors?.filter(
+        (e) =>
+          e.keyword === 'additionalProperties' ||
+          e.keyword === 'unevaluatedProperties'
+      ) ?? []
+    for (const error of additionalPropertiesErrors) {
+      const propertyName =
+        error.params.additionalProperty ?? error.params.unevaluatedProperty
+      ctx.warnings.push({
+        instancePath: `${error.instancePath}/${propertyName}`,
+        message: `property "${propertyName}" is not defined in the schema`,
+      })
+    }
+  }
+
+  // Part 2: warn about unsupported CSAF Extensions
+  for (const path of X_EXTENSIONS_PATHS) {
+    await walkPath(doc, path, async (instancePath, value) => {
+      const schemaUrl =
+        value && typeof value === 'object' && '$schema' in value
+          ? value.$schema
+          : undefined
+
+      if (typeof schemaUrl !== 'string') return
+
+      const isSupported = typeof csafAjv.getSchema(schemaUrl) === 'function'
+      if (isSupported) return
+
+      ctx.warnings.push({
+        instancePath: `${instancePath}/$schema`,
+        message: `unsupported CSAF Extension of schema "${schemaUrl}" (class: ${classifyExtensionSchema(
+          schemaUrl
+        )})`,
+      })
+    })
+  }
+
+  return ctx
 }
diff --git a/tests/csaf_2_1/oasis.js b/tests/csaf_2_1/oasis.js
index 3cd9fcaf..e8dfbbbc 100644
--- a/tests/csaf_2_1/oasis.js
+++ b/tests/csaf_2_1/oasis.js
@@ -17,7 +17,6 @@ const excluded = [
   '6.1.59',
   '6.1.60.2',
   '6.1.60.3',
-  '6.2.20',
   '6.2.24',
   '6.2.26',
   '6.2.31',
diff --git a/tests/csaf_2_1/recommendedTest_6_2_20.js b/tests/csaf_2_1/recommendedTest_6_2_20.js
new file mode 100644
index 00000000..ff86a39e
--- /dev/null
+++ b/tests/csaf_2_1/recommendedTest_6_2_20.js
@@ -0,0 +1,122 @@
+import { recommendedTest_6_2_20 } from '../../csaf_2_1/recommendedTests.js'
+
+const SCHEMA_URL = 'https://example.com/my-extension/schema/1.0.0.json'
+
+describe('recommendedTest_6_2_20', function () {
+  it('only runs on relevant documents', async function () {
+    expect(
+      (await recommendedTest_6_2_20({ vulnerabilities: 'mydoc' })).warnings
+        .length
+    ).to.equal(0)
+  })
+
+  it('warns for x_extensions at root level', async function () {
+    const doc = {
+      x_extensions: [{ $schema: SCHEMA_URL }],
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal('/x_extensions/0/$schema')
+    expect(result.warnings[0].message).to.contain(SCHEMA_URL)
+    expect(result.warnings[0].message).to.contain('class: unknown')
+  })
+
+  it('warns for x_extensions in document', async function () {
+    const doc = {
+      document: {
+        x_extensions: [{ $schema: SCHEMA_URL }],
+      },
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/document/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in product_tree/full_product_names', async function () {
+    const doc = {
+      product_tree: {
+        full_product_names: [{ x_extensions: [{ $schema: SCHEMA_URL }] }],
+      },
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/product_tree/full_product_names/0/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in product_tree/branches', async function () {
+    const doc = {
+      product_tree: {
+        branches: [{ product: { x_extensions: [{ $schema: SCHEMA_URL }] } }],
+      },
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/product_tree/branches/0/product/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in nested product_tree/branches', async function () {
+    const doc = {
+      product_tree: {
+        branches: [
+          {
+            branches: [
+              { product: { x_extensions: [{ $schema: SCHEMA_URL }] } },
+            ],
+          },
+        ],
+      },
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/product_tree/branches/0/branches/0/product/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in product_tree/product_paths', async function () {
+    const doc = {
+      product_tree: {
+        product_paths: [
+          { full_product_name: { x_extensions: [{ $schema: SCHEMA_URL }] } },
+        ],
+      },
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/product_tree/product_paths/0/full_product_name/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in vulnerabilities', async function () {
+    const doc = {
+      vulnerabilities: [{ x_extensions: [{ $schema: SCHEMA_URL }] }],
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/vulnerabilities/0/x_extensions/0/$schema'
+    )
+  })
+
+  it('warns for x_extensions in vulnerabilities/metrics/content', async function () {
+    const doc = {
+      vulnerabilities: [
+        {
+          metrics: [{ content: { x_extensions: [{ $schema: SCHEMA_URL }] } }],
+        },
+      ],
+    }
+    const result = await recommendedTest_6_2_20(doc)
+    expect(result.warnings.length).to.equal(1)
+    expect(result.warnings[0].instancePath).to.equal(
+      '/vulnerabilities/0/metrics/0/content/x_extensions/0/$schema'
+    )
+  })
+})