Sit without holding the dress in position
Sit on an ordinary chair and initially let the fabric fall naturally. Check whether the hem stays at a position you find comfortable and whether the neckline opens more than expected. Needing to hold the dress continually with one hand is a relevant observation for the occasion you have planned.
On a wrap dress, the overlap may sit differently when seated. Test whether it provides the coverage you want. Avoid repeatedly tightening a tie to compensate for another area. If you intend to wear a slip underneath, include it in the test and check that it does not ride up beneath the dress.
Walk with your normal stride
Take a few steps and turn around. A narrow skirt section may limit stride, while fuller fabric may gather between the legs. Movement reveals both. Any split should work as you intend while walking rather than merely looking appropriate when standing still.
If stairs are part of your day, carefully try a low step or a comparable movement somewhere safe. Hold the hem if that is how you would manage stairs later. A long dress does not need to suit every activity equally; its requirements need to fit the plan you actually have.
Include arms and pockets
Reach forwards and raise your arms through an ordinary movement. Sleeveless designs reveal how their arm openings sit; sleeved ones may pull across the shoulders or back. Notice whether the dress settles afterwards or requires substantial rearranging.
If there are pockets, try them with a light item you would genuinely carry. A heavy phone can change the drape. Decide whether you want to use the pockets for that object or carry a bag instead. A pocket's existence does not mean every item will sit in it without affecting the garment.
Keep the occasion as your reference
A dress for a largely seated meal has different demands from one for a day involving long walks. Note which movements felt comfortable and which limitations you would consciously accept. If those limitations prevent your actual plans, another shape is a more useful comparison than hoping the dress will behave differently by itself.
