diff --git a/tests/ecmascript/test-dev-ondemand-constructor-prototype-defineproperty.js b/tests/ecmascript/test-dev-ondemand-constructor-prototype-defineproperty.js
new file mode 100644
index 0000000000..da3d6f5694
--- /dev/null
+++ b/tests/ecmascript/test-dev-ondemand-constructor-prototype-defineproperty.js
@@ -0,0 +1,66 @@
+/*---
+{
+    "custom": true
+}
+---*/
+
+/*===
+- Object.defineProperty() and .prototype
+TypeError
+number 321
+number 123
+TypeError
+done
+===*/
+
+// Because the .prototype is intended to be writable, but configurable or
+// enumerable, Object.defineProperty() should not allow modification of
+// any attributes except: (1) to disable writable, (2) to update the value.
+print('- Object.defineProperty() and .prototype');
+try {
+    // This must fail because the (actually non-existent) .prototype is
+    // not configurable.
+    var X = function () {};
+    Object.defineProperty(X, 'prototype', { enumerable: true });
+    print('never here');
+} catch (e) {
+    print(e.name);
+}
+try {
+    // This must succeed because the .prototype is writable.
+    var X = function () {};
+    Object.defineProperty(X, 'prototype', { value: 321 });
+    print(typeof X.prototype, X.prototype);
+} catch (e) {
+    print(e);
+}
+try {
+    // Defining all attributes which are compatible with the virtualized
+    // existing ones -> must succeed.
+    var X = function () {};
+    Object.defineProperty(X, 'prototype', {
+        value: 123,
+        writable: true,
+        enumerable: false,
+        configurable: false
+    });
+    print(typeof X.prototype, X.prototype);
+} catch (e) {
+    print(e);
+}
+try {
+    // Defining all attributes which are incompatible with the virtualized
+    // existing ones -> must fail.
+    var X = function () {};
+    Object.defineProperty(X, 'prototype', {
+        value: 123,
+        writable: true,
+        enumerable: true,  // incompatible
+        configurable: false
+    });
+    print('never here');
+} catch (e) {
+    print(e.name);
+}
+
+print('done');
diff --git a/tests/ecmascript/test-dev-ondemand-constructor-prototype-getownpropertydescriptor.js b/tests/ecmascript/test-dev-ondemand-constructor-prototype-getownpropertydescriptor.js
new file mode 100644
index 0000000000..3427f8338d
--- /dev/null
+++ b/tests/ecmascript/test-dev-ondemand-constructor-prototype-getownpropertydescriptor.js
@@ -0,0 +1,26 @@
+/*---
+{
+    "custom": true
+}
+---*/
+
+/*===
+- Object.getOwnPropertyDescriptor() spawns .prototype
+object
+object
+true
+false
+false
+done
+===*/
+
+print('- Object.getOwnPropertyDescriptor() spawns .prototype');
+var X = function () {};
+var pd = Object.getOwnPropertyDescriptor(X, 'prototype');
+print(typeof pd);
+print(typeof pd.value);
+print(pd.writable);
+print(pd.enumerable);
+print(pd.configurable);
+
+print('done');
diff --git a/tests/ecmascript/test-dev-ondemand-constructor-prototype-misc.js b/tests/ecmascript/test-dev-ondemand-constructor-prototype-misc.js
new file mode 100644
index 0000000000..a63a9bcd1c
--- /dev/null
+++ b/tests/ecmascript/test-dev-ondemand-constructor-prototype-misc.js
@@ -0,0 +1,23 @@
+/*---
+{
+    "custom": true
+}
+---*/
+
+print('- non-constructable built-ins have no .prototype');
+var X = Math.cos;
+print('prototype' in X);
+print(X.prototype);
+print('prototype' in X);
+
+print('- non-constructable functions like object getter/setters have no .prototype');
+var tmp = {
+    get X() {},
+};
+X = Object.getOwnPropertyDescriptor(tmp, 'X').get;
+print(typeof X);
+print('prototype' in X);
+print(X.prototype);
+print('prototype' in X);
+
+print('done');
diff --git a/tests/ecmascript/test-dev-ondemand-constructor-prototype-refcount-finalize.js b/tests/ecmascript/test-dev-ondemand-constructor-prototype-refcount-finalize.js
new file mode 100644
index 0000000000..ddf7a85328
--- /dev/null
+++ b/tests/ecmascript/test-dev-ondemand-constructor-prototype-refcount-finalize.js
@@ -0,0 +1,72 @@
+/*---
+{
+    "custom": true
+}
+---*/
+
+function FX() {
+    print('finalize X');
+}
+function FY() {
+    print('finalize Y');
+}
+
+print('- prototype in func');
+var f = function () {};
+print('prototype' in f);
+Duktape.gc(); Duktape.gc();
+
+print('- own property names');
+var f = function () {};
+print(Object.getOwnPropertyNames(f).join(','));
+f.prototype.foo = 'bar';
+print(Object.getOwnPropertyNames(f).join(','));
+Duktape.gc(); Duktape.gc();
+
+print('- refcount finalization, anonymous function');
+var X = function () {};
+Duktape.fin(X, FX);
+print('setting X to null');
+X = null;
+print('X set to null');
+Duktape.gc(); Duktape.gc();
+
+print('- refcount finalization, named function');
+var X = function foo() {};
+Duktape.fin(X, FX);
+print('setting X to null');
+X = null;
+print('X set to null');
+Duktape.gc(); Duktape.gc();
+
+print('- refcount finalization, anonymous inner function, reference not kept');
+var X = function () {
+    var Y = function () {};
+    Duktape.fin(Y, FY);
+    Y = null;
+};
+Duktape.fin(X, FX);
+print('call X');
+X();
+print('setting X to null');
+X = null;
+print('X set to null');
+Duktape.gc(); Duktape.gc();
+
+print('- refcount finalization, anonymous inner function, reference kept');
+var X = function () {
+    var Y = function () {};
+    Duktape.fin(Y, FY);
+    // At this point the anonymous inner function points to the outer scope,
+    // which holds a reference back to the function via 'Y', so cannot
+    // collect via refcounting.
+};
+Duktape.fin(X, FX);
+print('call X');
+X();
+print('setting X to null');
+X = null;
+print('X set to null');
+Duktape.gc(); Duktape.gc();
+
+print('done');