The gold standard for diagnosing achalasia is esophageal manometry. This method detects high lower esophageal sphincter pressure and insufficient or absent sphincter relaxation during swallowing. Other diagnostic tests include esophagography (barium swallow) and endoscopy. Esophagography reveals dilation of the upper esophagus and progressive narrowing towards the lower part (bird's beak appearance). During endoscopy, narrowing of the distal esophagus and findings such as fungal esophagitis, which may develop due to food stasis, can be observed.