The compound which contains $–\mathrm{C}\mathrm{O}\mathrm{C}{\mathrm{H}}_3$ group in its structure, give positive iodoform test and the compound which contains $–\mathrm{C}\mathrm{H}\mathrm{O}\mathrm{ }$group give positive Fehling test.

In ethanal, $\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{H}\mathrm{O}$ both the groups are present, hence it responds to both iodoform test and Fehling's test.

Iodoform test

$\mathrm{C}{\mathrm{H}}_3\mathrm{C}\mathrm{H}\mathrm{O}+{\mathrm{I}}_2+\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\to \mathrm{C}\mathrm{H}{\mathrm{I}}_3+\mathrm{N}\mathrm{a}\mathrm{I}+{\mathrm{H}}_2\mathrm{O}$

Fehling's test 

${\text{CH}}_{\text{3}}\text{CHO}+\text{Cu}{\left(\text{OH}\right)}_{\text{2}}\to {\text{CH}}_{\text{2}}\text{COOH}+\underset{\left(\text{red}\text{ppt}\text{.}\right)}{{\text{Cu}}_{\text{2}}\text{O}\downarrow }+2{\text{H}}_{\text{2}}\text{O}$