未涵盖 C# 8.0 单元测试开关表达式

Question

我正在为我的项目使用支持 switch 表达式的 C# 8.0。我最近正在构建一个单元测试项目并生成代码覆盖率报告。但似乎所有 switch 表达式都有问题。我的代码中有一些类似于以下内容的行：

private static string GenerateRequestUrl(Language language, WeatherDataType dataType) {
    var url = "https://data.weather.gov.hk/weatherAPI/opendata/weather.php?";

    url += language switch {
        Language.English => "lang=en",
        Language.TraditionalChinese => "lang=tc",
        Language.SimplifiedChinese => "lang=sc",
        _ => "lang=en"
    };

    url += dataType switch {
        WeatherDataType.LocalWeatherForecast => "&dataType=flw",
        WeatherDataType.NineDaysWeather => "&dataType=fnd"
    };

    return url;
}

而且我的测试方法涵盖了上述所有情况，但报告显示那些带有 switch 表达式的行没有被涵盖。就像在这张图片中： Coverage Highlights in JetBrains Rider

我应该怎么做才能使它们被覆盖。

Answer 1

虽然它可能不是您希望的答案，但代码覆盖率似乎不适用于非顺序开关表达式。

当您查看 IL 代码时，新的 C# 8.0 开关表达式首先计算（跳转）哪个表达式为真，然后设置 url。
而顺序 switch 语句在 case 语句之后设置 url。

因此，如果您想要全面覆盖，您应该使用顺序 switch 语句（例如下面代码中的 WeatherDataType）。

代码

IL 代码

    .method public hidebysig static string  GenerateRequestUrl(valuetype Demo.Generator/Language language,
                                                           valuetype Demo.Generator/WeatherDataType dataType) cil managed
{
  // Code size       130 (0x82)
  .maxstack  2
  .locals init (string V_0,
           string V_1,
           string V_2,
           valuetype Demo.Generator/WeatherDataType V_3,
           valuetype Demo.Generator/WeatherDataType V_4,
           string V_5)
  IL_0000:  nop
  IL_0001:  ldstr      "https://data.weather.gov.hk/weatherAPI/opendata/we"
  + "ather.php\?"
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  stloc.1
  IL_0009:  ldc.i4.1
  IL_000a:  brtrue.s   IL_000d
  IL_000c:  nop
  IL_000d:  ldarg.0
  IL_000e:  switch     ( 
                        IL_0021,
                        IL_0029,
                        IL_0031)
  IL_001f:  br.s       IL_0039
  IL_0021:  ldstr      "lang=en"
  IL_0026:  stloc.2
  IL_0027:  br.s       IL_0041
  IL_0029:  ldstr      "lang=tc"
  IL_002e:  stloc.2
  IL_002f:  br.s       IL_0041
  IL_0031:  ldstr      "lang=sc"
  IL_0036:  stloc.2
  IL_0037:  br.s       IL_0041
  IL_0039:  ldstr      "lang=en"
  IL_003e:  stloc.2
  IL_003f:  br.s       IL_0041
  IL_0041:  ldc.i4.1
  IL_0042:  brtrue.s   IL_0045
  IL_0044:  nop
  IL_0045:  ldloc.1
  IL_0046:  ldloc.2
  IL_0047:  call       string [System.Runtime]System.String::Concat(string,
                                                                    string)
  IL_004c:  stloc.0
  IL_004d:  ldarg.1
  IL_004e:  stloc.s    V_4
  IL_0050:  ldloc.s    V_4
  IL_0052:  stloc.3
  IL_0053:  ldloc.3
  IL_0054:  brfalse.s  IL_005e
  IL_0056:  br.s       IL_0058
  IL_0058:  ldloc.3
  IL_0059:  ldc.i4.1
  IL_005a:  beq.s      IL_006c
  IL_005c:  br.s       IL_007a
  IL_005e:  ldloc.0
  IL_005f:  ldstr      "&dataType=flw"
  IL_0064:  call       string [System.Runtime]System.String::Concat(string,
                                                                    string)
  IL_0069:  stloc.0
  IL_006a:  br.s       IL_007a
  IL_006c:  ldloc.0
  IL_006d:  ldstr      "&dataType=fnd"
  IL_0072:  call       string [System.Runtime]System.String::Concat(string,
                                                                    string)
  IL_0077:  stloc.0
  IL_0078:  br.s       IL_007a
  IL_007a:  ldloc.0
  IL_007b:  stloc.s    V_5
  IL_007d:  br.s       IL_007f
  IL_007f:  ldloc.s    V_5
  IL_0081:  ret
} // end of method Generator::GenerateRequestUrl