FormattableString, why are you so cruel to Eastern Europeans?

tests/ImageSharp.Tests/TestUtilities/ImagingTestCaseUtility.cs

@@ -89,6 +89,8 @@ namespace SixLabors.ImageSharp.Tests
             return $"{this.GetTestOutputDir()}/{this.TestName}{pixName}{fn}{details}{extension}";
         }
 
+        private static string Inv(FormattableString formattable) => System.FormattableString.Invariant(formattable);
+        
         /// <summary>
         /// Gets the recommended file name for the output of the test
         /// </summary>
@@ -111,14 +113,16 @@ namespace SixLabors.ImageSharp.Tests
                 TypeInfo info = type.GetTypeInfo();
                 if (info.IsPrimitive || info.IsEnum || type == typeof(decimal))
                 {
-                    detailsString =  string.Format(System.Globalization.CultureInfo.InvariantCulture, "{0}", testOutputDetails);
+                    detailsString = Inv($"{testOutputDetails}");
                 }
                 else
                 {
                     IEnumerable<PropertyInfo> properties = testOutputDetails.GetType().GetRuntimeProperties();
 
-                    detailsString = String.Join(
+                    detailsString = string.Join(
-                        "_", properties.ToDictionary(x => x.Name, x => string.Format(System.Globalization.CultureInfo.InvariantCulture, "{0}", x.GetValue(testOutputDetails))).Select(x => $"{x.Key}-{x.Value}")
+                        "_",
+                        properties.ToDictionary(x => x.Name, x => x.GetValue(testOutputDetails))
+                            .Select(x => Inv($"{x.Key}-{x.Value}"))
                         );
                 }
             }