Why can't I iterate over an array using map. TypeError: test.map is not a function?

Question

React

I get data from firebase via axios and I want to render it

The data comes to the render function as an array of objects
Here I put it in the console:

render() {  
        const test = this.props.users;
        console.log('test', test);

        return (
            <div>
                 {
                    test.map(u => { 
                    return <div key={u.id}>
                             <div>{u.fullName}</div>
                           </div>
                        })
                }
            </div>
        )
    }

If the same data is output from the component, everything works

render() {
        const dataFromComponent = [  
                {id: 1, fullName: 'Max' },
                {id: 2,  fullName: 'Jordan' },
                {id: 3,  fullName: 'Gary' },
                {id: 4,  fullName: 'Oleg' } 
                ]

        return (
            <div>
                 {
                    dataFromComponent.map(u => { 
                    return <div key={u.id}>
                             <div>{u.fullName}</div>
                           </div>
                        })
                }
            </div>
        )
    }

On output:

if (!test.map ) {
            console.log("props", {...this.props})
        }

falls into the console:

Answer 1

Are you sure that at some stage of the life cycle your test is not undefined?
https://reactjs.org/docs/state-and-lifecycle.html
https://reactjs.org/docs/conditional-rendering.html