diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index 555c46c..c911206 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -975,6 +975,28 @@
     Check()
   END
   v9.CheckSourceSuccess(lines)
+
+  # Try using "this." argument in a class method
+  lines =<< trim END
+    vim9script
+    class A
+      this.val = 10
+      static def Foo(this.val: number)
+      enddef
+    endclass
+  END
+  v9.CheckSourceFailure(lines, 'E1390: Cannot use an object variable "this.val" except with the "new" method', 4)
+
+  # Try using "this." argument in an object method
+  lines =<< trim END
+    vim9script
+    class A
+      this.val = 10
+      def Foo(this.val: number)
+      enddef
+    endclass
+  END
+  v9.CheckSourceFailure(lines, 'E1390: Cannot use an object variable "this.val" except with the "new" method', 4)
 enddef
 
 def Test_class_object_member_inits()
@@ -1722,7 +1744,7 @@
     var a = A.new()
     var v = a.bar
   END
-  v9.CheckSourceFailure(lines, 'E1326: Variable not found on object "A": bar', 5)
+  v9.CheckSourceFailure(lines, 'E1337: Class variable "bar" not found in class "A"', 5)
 enddef
 
 " These messages should show the defining class of the variable (base class),
@@ -4255,7 +4277,7 @@
     var a = A.new()
     a._Foo()
   END
-  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo()', 9)
+  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo', 9)
 
   # Try calling a private method using an object (from a def function)
   lines =<< trim END
@@ -4468,7 +4490,7 @@
     var c = C.new()
     assert_equal(1234, c._Foo())
   END
-  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo()', 16)
+  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo', 16)
 
   # Using "_" prefix in a method name should fail outside of a class
   lines =<< trim END
@@ -4494,7 +4516,7 @@
     endclass
     A._Foo()
   END
-  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo()', 8)
+  v9.CheckSourceFailure(lines, 'E1366: Cannot access private method: _Foo', 8)
 
   # Try calling a class private method (from a def function)
   lines =<< trim END
@@ -5122,7 +5144,7 @@
     var a = A.new()
     echo a.svar2
   END
-  v9.CheckSourceFailure(lines, 'E1375: Class variable "svar2" accessible only using class "A"', 8)
+  v9.CheckSourceFailure(lines, 'E1337: Class variable "svar2" not found in class "A"', 8)
 
   # Cannot write to a class variable using an object in script context
   lines =<< trim END
@@ -5597,7 +5619,7 @@
     var a = A.new()
     var i = a.val
   END
-  v9.CheckSourceFailure(lines, 'E1375: Class variable "val" accessible only using class "A"', 7)
+  v9.CheckSourceFailure(lines, 'E1337: Class variable "val" not found in class "A"', 7)
 
   # Modifying a class variable using an object at function level
   lines =<< trim END
@@ -5969,6 +5991,18 @@
   END
   v9.CheckSourceSuccess(lines)
 
+  # extending empty interface
+  lines =<< trim END
+    vim9script
+    interface A
+    endinterface
+    interface B extends A
+    endinterface
+    class C implements B
+    endclass
+  END
+  v9.CheckSourceSuccess(lines)
+
   lines =<< trim END
     vim9script
     interface A
@@ -6567,6 +6601,17 @@
       o.F()
     END
     v9.CheckSourceFailure(lines, $'E1034: Cannot use reserved name {kword}', 3)
+
+    # class variable name
+    if kword != 'this'
+      lines =<< trim eval END
+        vim9script
+        class C
+          public static {kword}: list<number> = [1, 2, 3]
+        endclass
+      END
+      v9.CheckSourceFailure(lines, $'E1034: Cannot use reserved name {kword}', 3)
+    endif
   endfor
 enddef