你不需要测试BufferedReader，这里也不能使用Mockito，因为你需要在代码中手动示例化对象。你只需要将代码拆分：将阅读逻辑移到新方法中（例如readCsvFile()），然后为它编写测试。

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.stereotype.Component;

@Component
public class Cache implements InitializingBean {
    private static Map<String, String> map = new HashMap<>();

    @Override
    public void afterPropertiesSet() {
        map.putAll(readCsvFile("file.csv"));
    }

    // readCsvFile can be easily tested
    static Map<String, String> readCsvFile(final String fileName) {
        final Map<String, String> buffer = new HashMap<>();
        try (BufferedReader reader = new BufferedReader(new FileReader(fileName))) {
            String details;
            while ((details = reader.readLine()) != null) {
                String[] values = details.split(",", 2);

                String firstString = values[0];
                String secondString = values[1];
                buffer.put(firstString, secondString);
            }
        } catch (IOException ex) {
            //ex.printStackTrace();
            // TODO better log exception here
        }
        return buffer;
    }
}

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然后，您可以为该高速缓存bean编写一个测试，使其在启动后不为空