Most likely you don't need it, since
private methods do not need to Moka, in the General case. Moka methods EXTERNAL dependencies
But if right need, then the current object (the method by which testite inherently) is also creating through the IOC-bilder. That is the test class becomes MOK. And make the method under test with the exception, that is, its Moka Moka do not need and it will work as it is...
Example (do not forget about the AAA methodology):
// Arrange
$provider = $this
->getMockBuilder(UserProvider::class)
->setMethodsExcept(['delete']) // these methods will be present here, though the IOC
->setConstructorArgs([]) // here based on the constructor to pass
->getMock();
$provider = $provider
->expects($this->once())
->method('canDelete') // makeem private method
->willReturn(true);
// Action
$result = $provider->delete();
// Assert
$this->assertEquals(true, $result);