Amortization of €11 million, €8 million and €5 million in 2018, 2017, and 2016, respectively, is included in research and development in the consolidated statement of operations. Research and development costs that are not eligible for capitalization have been expensed in the period incurred.

Goodwill is tested for impairment on an annual basis or when there are indications the carrying amount may be impaired. Goodwill is allocated to the Group’s two operating segments, Premium and Ad-Supported, based on the units that are expected to benefit from the business combination. The Group monitors goodwill at the operating segment level for internal purposes, consistent with the way it assesses performance and allocates resources. The carrying amount of goodwill allocated to each of the operating segments is as follows:

The detailed calculations of recoverable amounts performed in 2016, which noted substantial headroom, were used in the 2018 impairment test as there have been no adverse significant changes in the industry and competitive environment, market capitalization, stock price and overall financial performance such that the recoverable amounts would be less than the carrying amount in 2018. Therefore, the Group concluded that goodwill was not impaired.