solidity/test/libsolidity/syntaxTests/inheritance/override/override_multiple.sol

abstract contract A {
	function foo() internal virtual returns (uint256);
	function test(uint8 _a) internal virtual returns (uint256) {}
}
abstract contract B {
	function foo() internal virtual returns (uint256);
	function test() internal virtual returns (uint256);
}
abstract contract C {
	function foo() internal virtual returns (uint256);
}
abstract contract D {
	function foo() internal virtual returns (uint256);
}
contract X is A, B, C, D {
	int public override testvar;
	function test() internal override returns (uint256) {}
	function foo() internal override(A, B, C, D) returns (uint256) {}
}