JS: move expressions test to box tests

js/js.translator/testData/box/expression/equals/compareToNullWithCustomEquals.kt

@@ -0,0 +1,16 @@
+package foo
+
+class A {
+    override fun equals(other: Any?) = super.equals(other)
+}
+
+fun box(): String {
+    val a: A? = null
+
+    testTrue { a == null }
+    testFalse { a != null }
+    testTrue { null == a }
+    testFalse { null != a }
+
+    return "OK"
+}