Add more tests

Author: liufengyun

tests/init/neg/i15764b.scala

@@ -0,0 +1,7 @@
+class B(val y: Int):
+  // println(y)
+  // foo()
+  def foo() = println(y)
+
+class C(x: Int) extends B(x):
+  override val y: Int = x      // error: override param with non-param

tests/init/neg/i15764c.scala

@@ -0,0 +1,5 @@
+class A(val y: Int)
+
+class B(override val y: Int) extends A(y)
+
+class C(override val y: Int) extends B(7)  // error