The emulsion test is a method to determine the presence of lipids using wet chemistry. The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water. Since lipids do not dissolve in water, when the ethanol is diluted, it falls out of solution to give a cloudy white emulsion.
Add Ethanol to the solution you want to test, add water. A colour change to cloudy white shows lipids are present.
References
Emulsion test Wikipedia(Text) CC BY-SA