In a courthouse in Portland, Ore., the federal government is challenging the biggest supermarket consolidation in U.S. history.

A dozen miles away, in a neighborhood called Rockwood, there is an example of what is at stake.

Twenty-five years ago, three supermarkets served Rockwood. Just one, an Albertsons, still stands. With 40,000 people and one of the highest poverty rates in the region, Rockwood has become a food desert.

Serge Mutalimba used to shop at a Safeway; now he takes a bus ride that is about twice as long to the remaining Albertsons. “Everybody else is gone,” said Mr. Mutalimba, who has lived in and around Rockwood for more than two decades. “They’re all completely gone.”

The fate of the Albertsons where Mr. Mutalimba shops could be determined by a trial that’s underway in Portland. Kroger, the country’s largest supermarket chain, has made a $24.6 billion bid to buy the Albertsons chain. While Kroger says no stores would be shut down, the Federal Trade Commission has sued to block the acquisition, saying it would mean less competition in the grocery industry. The likely result, it argues, would be higher prices and store closings.

The hearing before a federal judge to determine if the deal can go through is expected to last until Friday.

Rockwood is dotted with low-rise apartment buildings and connected to central Portland through light rail and bus lines. Racially and ethnically diverse, it was shaped by gentrification; as housing costs rose in Portland, poorer families were pushed to the outskirts of the city and places like Rockwood. About a quarter of Rockwood’s residents identify as Latino, and at a local food pantry on a recent afternoon, Spanish and Russian were spoken as much as English in the line for groceries.