diff --git a/src/utils/class.js b/src/utils/class.js
index 6b062d90..ca1072d9 100644
--- a/src/utils/class.js
+++ b/src/utils/class.js
@@ -37,28 +37,28 @@ export function extendClassStaticProps(childClass, parentClass, excludedProps =
 }
 
 /**
- * Extends an object with a parent class namespace.
+ * Slightly different implementation of extendClass assuming excludedProps
+ * is contained within the child-most class definition and assigning only
+ * the most recent props rather than the most distant props.
  * See extendClass.
- * TODO : match call signature with extendClass and
- *        make use of getPrototypeOf rather than __proto__
- *        but verify correctness in additional use cases first
  */
-export function extendThis(child, childClass, parentClass, excludedProps = [], ...args) {
-    let props;
-    let obj = new parentClass.prototype.constructor(...args);
+export function extendThis(childClass, parentClass, config) {
+    let props, protos;
+    let obj = new parentClass.prototype.constructor(config);
     const exclude = ["constructor", ...Object.getOwnPropertyNames(childClass.prototype)];
     const seen = []; // remember most recent occurrence of prop name (like inheritance)
-    while (obj.__proto__) {
-        props = Object.getOwnPropertyNames(obj.__proto__);
+    while (Object.getPrototypeOf(obj)) {
+        protos = Object.getPrototypeOf(obj);
+        props = Object.getOwnPropertyNames(protos);
         props.filter(p => !exclude.includes(p)).map((prop) => {
             if (seen.includes(prop)) return;
-            const getter = obj.__lookupGetter__(prop);
-            const setter = obj.__lookupSetter__(prop);
-            if (getter) child.__defineGetter__(prop, getter);
-            if (setter) child.__defineSetter__(prop, setter);
-            if (!(getter || setter)) child[prop] = obj[prop];
+            const getter = protos.__lookupGetter__(prop);
+            const setter = protos.__lookupSetter__(prop);
+            if (getter) childClass.prototype.__defineGetter__(prop, getter);
+            if (setter) childClass.prototype.__defineSetter__(prop, setter);
+            if (!(getter || setter)) childClass.prototype[prop] = protos[prop];
             seen.push(prop);
         })
-        obj = obj.__proto__;
+        obj = protos;
     }
 }
diff --git a/tests/utils.class.js b/tests/utils.class.js
new file mode 100644
index 00000000..0616d282
--- /dev/null
+++ b/tests/utils.class.js
@@ -0,0 +1,133 @@
+import { mix } from "mixwith";
+import { expect } from "chai";
+import { InMemoryEntity, NamedInMemoryEntity, DefaultableMixin, RuntimeItemsMixin } from "../src/entity";
+import { deepClone } from "../src/utils/clone";
+import { extendClass, extendThis } from "../src/utils/class";
+
+
+class BaseEntity extends mix(InMemoryEntity).with(RuntimeItemsMixin) {
+
+    constructor(config) {
+        super(config);
+    }
+
+    baseMethod() {
+        return "base";
+    }
+
+}
+
+
+class ExtendClassEntity extends mix(NamedInMemoryEntity).with(DefaultableMixin) {
+
+    constructor(config, excluded = []) {
+        super(config);
+        extendClass(ExtendClassEntity, BaseEntity, excluded, [config]);
+
+    }
+
+    baseMethod() {
+        return "derived";
+    }
+
+}
+
+
+class BaseBetweenEntity extends NamedInMemoryEntity {
+
+    static staticAttr = "base";
+
+    constructor(config) {
+        super(config);
+        this.instanceAttr = "base";
+    }
+
+    betweenMethod() {
+        return "base";
+    }
+
+}
+
+
+class BetweenEntity extends BaseBetweenEntity {
+
+    static staticAttr = "between";
+
+    constructor(config) {
+        super(config);
+        this.instanceAttr = "between";
+    }
+
+    betweenMethod() {
+        return "between";
+    }
+}
+
+
+class ExtendThisEntity extends mix(BetweenEntity).with(DefaultableMixin) {
+
+    constructor(config, excluded = []) {
+        super(config);
+        extendThis(ExtendThisEntity, BaseEntity, config);
+
+    }
+
+    baseMethod() {
+        return "derived";
+    }
+
+}
+
+
+describe("extendClass", () => {
+
+    it("extends classes no excluded props", () => {
+        const obj = new ExtendClassEntity({});
+        expect(obj.baseMethod()).to.be.equal("base");
+    });
+
+    it("should support excluded props but doesnt", () => {
+        const obj = new ExtendClassEntity({});
+        expect(obj.baseMethod()).not.to.be.equal("derived");
+    });
+
+    it("should have results but doesnt", () => {
+        const obj = new ExtendClassEntity({"results": ["test"]});
+        expect(JSON.stringify(obj.results)).not.to.be.equal(JSON.stringify([{"name": "test"}]));
+    });
+
+});
+
+
+describe("extendThis", () => {
+
+    it("extends this prefer child method", () => {
+        const obj = new ExtendThisEntity({});
+        expect(obj.baseMethod()).to.be.equal("derived");
+    });
+
+    it("extends this support base mixins", () => {
+        const obj = new ExtendThisEntity({"results": ["test"]});
+        expect(JSON.stringify(obj.results)).to.be.equal(JSON.stringify([{"name": "test"}]));
+    });
+
+    it("remembers intermediate methods", () => {
+        const base = new BaseBetweenEntity();
+        expect(base.betweenMethod()).to.be.equal("base");
+        const obj = new ExtendThisEntity({});
+        expect(obj.betweenMethod()).to.be.equal("between");
+    });
+
+    it("propagates instance attributes", () => {
+        const base = new BaseBetweenEntity({});
+        expect(base.instanceAttr).to.be.equal("base");
+        const obj = new ExtendThisEntity({});
+        expect(obj.instanceAttr).to.be.equal("between");
+    });
+
+    it("propagates static attributes", () => {
+        expect(BaseBetweenEntity.staticAttr).to.be.equal("base");
+        expect(ExtendThisEntity.staticAttr).to.be.equal("between");
+    });
+
+});