Validation: Add immediate data pipeline validation tests

src/webgpu/api/validation/createPipelineLayout.spec.ts

@@ -512,3 +512,32 @@ g.test('bind_group_layouts,set_pipeline_with_null_bind_group_layouts')
       }
     }
   });
+
+g.test('immediate_data_size')
+  .desc(
+    `
+    Test that creating a pipeline layout with immediateSize validates:
+    - immediateSize must be a multiple of 4.
+    - immediateSize must be <= device.limits.maxImmediateSize.
+  `
+  )
+  .fn(t => {
+    const maxImmediateSize = t.device.limits.maxImmediateSize ?? 64;
+
+    const kTestSizes = [0, 4, maxImmediateSize, maxImmediateSize + 4, 1, 2, 3, 5];
+
+    for (const size of kTestSizes) {
+      const descriptor = {
+        bindGroupLayouts: [],
+        immediateSize: size,
+      };
+
+      const isMultipleOf4 = size % 4 === 0;
+      const isWithinLimit = size <= maxImmediateSize;
+      const shouldSucceed = isMultipleOf4 && isWithinLimit;
+
+      t.expectValidationError(() => {
+        t.device.createPipelineLayout(descriptor);
+      }, !shouldSucceed);
+    }
+  });