Why it is unit elasticity

If I always spend a total of exactly $$\\\10$$ per week on coffee, then does my demand function have unit elasticity?

According to me, the change in income doesn't affect my coffee consumption, so it does not seem like unit elasticity. Can someone help me understand this?

• Could you please clarify two points: 1) Do you mean exactly \\$10 per week whatever the price of coffee that week may be? 2) Are you asking about price elasticity of demand or income elasticity of demand? May 23 '21 at 12:48

$$Q^d(p)=10/p$$ (I always spend $$\\\ 10$$ on coffee, which buys me exactly $$10/p$$ units of coffee, where $$p$$ is the price of coffee).
$$\varepsilon \equiv \frac{dQ^d}{dp} \frac{p}{Q^d}$$