test: add unit tests for handling additionalProperties in API examples

- Introduced tests to ensure the application does not crash when handling additionalProperties, including scenarios with null and undefined properties.
- Verified that examples are generated correctly without "unknown" types and that the methods handle edge cases gracefully.
- Added regression tests to maintain compatibility with previous versions.

Author: alexpmule

test/additional-properties-fix.test.js

@@ -0,0 +1,162 @@
+import { fixture, assert, html } from '@open-wc/testing';
+import { AmfLoader } from './amf-loader.js';
+import '../api-example-generator.js';
+
+describe('Additional Properties Fix', () => {
+  async function basicFixture(amf) {
+    return (await fixture(html`<api-example-generator
+      .amf="${amf}"></api-example-generator>`));
+  }
+
+  const apiFile = 'v4_0_0_api_specs';
+
+  [
+    ['json+ld data model', false],
+    ['Compact data model', true]
+  ].forEach(([label, compact]) => {
+    describe(label, () => {
+      let element;
+      let amf;
+
+      before(async () => {
+        amf = await AmfLoader.load(compact, apiFile);
+      });
+
+      beforeEach(async () => {
+        element = await basicFixture(amf);
+      });
+
+      it('should handle additionalProperties without crashing', () => {
+        // This test reproduces the bug where additionalProperties caused 
+        // a crash due to properties being null/undefined
+        
+        // Look for a payload that uses ForceConfig schema which has additionalProperties: true
+        const payloads = AmfLoader.lookupPayload(
+          amf,
+          '/v4.0.0/messages',
+          'post'
+        );
+        
+        // This should not throw an error and should generate a valid example
+        const result = element.generatePayloadsExamples(
+          payloads,
+          'application/json'
+        );
+        
+        assert.typeOf(result, 'array', 'Should return an array of examples');
+        assert.isAbove(result.length, 0, 'Should have at least one example');
+        
+        const example = result[0];
+        assert.typeOf(example.value, 'string', 'Example should have a string value');
+        assert.isFalse(example.hasRaw, 'Should not be a raw example');
+        assert.isFalse(example.hasTitle, 'Should not have a title');
+        assert.isFalse(example.hasUnion, 'Should not be a union');
+        
+        // Verify it's valid JSON
+        assert.doesNotThrow(() => {
+          JSON.parse(example.value);
+        }, 'Generated example should be valid JSON');
+      });
+
+      it('should generate examples for schemas with additionalProperties: true', () => {
+        // Test specifically for schemas that have additionalProperties: true
+        // This tests the fix in _computeJsonObjectValue method
+        
+        const payloads = AmfLoader.lookupPayload(
+          amf,
+          '/v4.0.0/messages',
+          'post'
+        );
+        
+        const result = element.generatePayloadsExamples(
+          payloads,
+          'application/json'
+        );
+        
+        assert.typeOf(result, 'array');
+        const example = result[0];
+        
+        // The example should be generated successfully without "Unknown type"
+        assert.typeOf(example.value, 'string');
+        assert.notInclude(example.value.toLowerCase(), 'unknown', 'Should not contain "unknown" type');
+        
+        // Parse the JSON to verify structure
+        const parsedExample = JSON.parse(example.value);
+        assert.typeOf(parsedExample, 'object', 'Should generate a valid JSON object');
+      });
+
+      it('should handle _jsonExampleFromProperties with null properties gracefully', () => {
+        // This test verifies the specific fix: adding null check in _jsonExampleFromProperties
+        
+        // Test the method directly with null properties
+        const result = element._jsonExampleFromProperties(null);
+        assert.typeOf(result, 'object', 'Should return an empty object when properties is null');
+        assert.deepEqual(result, {}, 'Should return empty object for null properties');
+        
+        // Test with undefined properties
+        const result2 = element._jsonExampleFromProperties(undefined);
+        assert.typeOf(result2, 'object', 'Should return an empty object when properties is undefined');
+        assert.deepEqual(result2, {}, 'Should return empty object for undefined properties');
+        
+        // Test with empty array (should work as before)
+        const result3 = element._jsonExampleFromProperties([]);
+        assert.typeOf(result3, 'object', 'Should return an empty object for empty array');
+        assert.deepEqual(result3, {}, 'Should return empty object for empty properties array');
+      });
+
+      it('should handle _computeJsonObjectValue with additionalProperties correctly', () => {
+        // Test the _computeJsonObjectValue method directly to ensure it handles 
+        // additionalProperties scenarios without crashing
+        
+        // Create a mock range object similar to what would be generated for additionalProperties
+        const mockRange = {
+          [element._getAmfKey(element.ns.w3.shacl.property)]: null, // No regular properties
+          [element._getAmfKey(element.ns.w3.shacl.additionalPropertiesSchema)]: [
+            {
+              [element._getAmfKey(element.ns.w3.shacl.property)]: null // additionalProperties with null properties
+            }
+          ]
+        };
+        
+        // This should not crash and should return an empty object
+        const result = element._computeJsonObjectValue(mockRange);
+        assert.typeOf(result, 'object', 'Should return an object');
+        assert.deepEqual(result, {}, 'Should return empty object when no properties can be processed');
+      });
+
+      it('regression test: should work with version 4.4.27 behavior and beyond', () => {
+        // This is a regression test to ensure the fix maintains compatibility
+        // with the behavior that worked in version 4.4.27
+        
+        const payloads = AmfLoader.lookupPayload(
+          amf,
+          '/v4.0.0/messages',
+          'post'
+        );
+        
+        // Before the fix (4.4.28+), this would throw an error or return "Unknown type"
+        // After the fix, it should work correctly
+        assert.doesNotThrow(() => {
+          const result = element.generatePayloadsExamples(
+            payloads,
+            'application/json'
+          );
+          
+          assert.typeOf(result, 'array', 'Should successfully generate examples');
+          
+          if (result && result.length > 0) {
+            const example = result[0];
+            assert.typeOf(example.value, 'string', 'Should have a valid example value');
+            
+            // Ensure it doesn't contain "Unknown type" which was the reported issue
+            assert.notInclude(
+              example.value, 
+              'unknown-type', 
+              'Should not generate unknown-type in examples'
+            );
+          }
+        }, 'Should not throw errors when processing additionalProperties');
+      });
+    });
+  });
+});