我花了大约一个月的时间来解决这个问题。而解决方法是如此简单...
您只需要实现内存搜索并检查静态标志来调用它。
范例：

public static class UnitTestChecker
{
    public static bool IsTest { get; set; }
}

public static class PostgreSqlExtensions
{
    public static bool ILike(string input, string pattern)
    {
        if (UnitTestChecker.IsTest)
            return InMemoryExtensions.ILike(input, pattern);
        else
            return EF.Functions.ILike(input, pattern);
    }
}

public static class InMemoryExtensions
{
    private static readonly IReadOnlyDictionary<char, string> _patternMapping = new Dictionary<char, string>
    {
        { '%', ".*" },
        { '_', "?*" },
        { '\\', "" },
    };

    public static bool ILike(string input, string postgreSqlPattern)
    {
        var capacity = postgreSqlPattern.Length + postgreSqlPattern.Length / 2; // presumably
        var stringBuilder = new StringBuilder(capacity);

        foreach (var character in postgreSqlPattern)
        {
            if (_patternMapping.TryGetValue(character, out var newCharacters))
                stringBuilder.Append(newCharacters);
            else
                stringBuilder.Append(character);
        }

        var regexPattern = stringBuilder.ToString();
        var regex = new Regex(
            regexPattern,
            options: RegexOptions.IgnoreCase | RegexOptions.CultureInvariant,
            matchTimeout: TimeSpan.FromMilliseconds(50));

        return regex.IsMatch(input);
    }
}

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然后在代码中将EF.Functions.ILike替换为PostgreSqlExtensions.ILike。例如：

var mercedesCars = await _db.Cars
    .Where(x => PostgreSqlExtensions.ILike(x.Name, "Mercedes%"))
    .ToListAsync(cancellationToken);

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最后，在单元测试或初始测试设置中，只需设置标志：

if (!UnitTestChecker.IsTest)
    UnitTestChecker.IsTest = true;

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