chore: test missing nested span diff

Author: cedricziel

src/Utils/Test/tests/Unit/TraceStructureAssertionTraitTest.php

@@ -572,6 +572,81 @@ public function test_trace_structure_diff_output_with_missing_root_span(): void
         }
     }
 
+    /**
+     * Test that the diff output is generated correctly when a nested child span is missing.
+     */
+    public function test_trace_structure_diff_output_with_missing_nested_span(): void
+    {
+        $tracer = $this->tracerProvider->getTracer('test-tracer');
+
+        // Create a root span
+        $rootSpan = $tracer->spanBuilder('root-span')
+            ->setSpanKind(SpanKind::KIND_SERVER)
+            ->startSpan();
+
+        // Activate the root span
+        $rootScope = $rootSpan->activate();
+
+        try {
+            // Create only one child span
+            $childSpan = $tracer->spanBuilder('child-span-1')
+                ->setSpanKind(SpanKind::KIND_INTERNAL)
+                ->startSpan();
+            $childSpan->setAttribute('attribute.one', 'value1');
+            $childSpan->end();
+        } finally {
+            $rootSpan->end();
+            $rootScope->detach();
+        }
+
+        // Define an expected structure with two child spans
+        $expectedStructure = [
+            [
+                'name' => 'root-span',
+                'kind' => SpanKind::KIND_SERVER,
+                'children' => [
+                    [
+                        'name' => 'child-span-1',
+                        'kind' => SpanKind::KIND_INTERNAL,
+                        'attributes' => [
+                            'attribute.one' => 'value1',
+                        ],
+                    ],
+                    [
+                        'name' => 'child-span-2', // This span doesn't exist
+                        'kind' => SpanKind::KIND_CLIENT,
+                        'attributes' => [
+                            'attribute.two' => 42,
+                        ],
+                    ],
+                ],
+            ],
+        ];
+
+        try {
+            // This should fail
+            $this->assertTraceStructure($this->storage, $expectedStructure);
+            $this->fail('Expected assertion to fail but it passed');
+        } catch (\PHPUnit\Framework\AssertionFailedError $e) {
+            // Verify that the error message contains the diff
+            $errorMessage = $e->getMessage();
+
+            // Check for diff markers
+            $this->assertStringContainsString('--- Expected Trace Structure', $errorMessage);
+            $this->assertStringContainsString('+++ Actual Trace Structure', $errorMessage);
+
+            // Check for specific content in the diff
+            $this->assertStringContainsString('root-span', $errorMessage);
+            $this->assertStringContainsString('child-span-1', $errorMessage);
+
+            // Check for the missing child span indicator in the diff
+            $this->assertStringContainsString('[1] => Array', $errorMessage);
+
+            // Check that the error message indicates a missing span
+            $this->assertStringContainsString('No matching span found', $errorMessage);
+        }
+    }
+
     /**
      * Test asserting a trace structure using PHPUnit matchers.
      */