dotnet-installer/test/EndToEnd/SupportedNetCoreAppVersions.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace EndToEnd
{
    public static class TargetFrameworkHelper
    {
        private static Version _firstNetAppVersion = new Version(5, 0);

        public static IEnumerable<string> GetNetAppTargetFrameworks(IEnumerable<string> versions) =>
            versions.Select(v => $"netcoreapp{v}")
                    // Add netX.X tfms starting with 5.0
                    .Concat(versions.Where(v => Version.Parse(v) >= _firstNetAppVersion).Select(v => $"net{v}"));
    }

    public class SupportedNetCoreAppVersions : IEnumerable<object[]>
    {
        public IEnumerator<object[]> GetEnumerator() => Versions.Select(version => new object[] { version }).GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
        public static IEnumerable<string> Versions => new[]
        {
            "1.0",
            "1.1",
            "2.0",
            "2.1",
            "2.2",
            "3.0",
            "3.1",
            "5.0",
            "6.0",
            "7.0",
            "8.0",
            "9.0"
        };

        public static IEnumerable<string> TargetFrameworkShortFolderVersion
        {
            get
            {
                var targetFrameworkShortFolderVersion = new List<string>();
                foreach (var v in Versions)
                {
                    if (Version.Parse(v).Major >= 5)
                    {
                        targetFrameworkShortFolderVersion.Add($"net{v}");
                    }
                    else
                    {
                        targetFrameworkShortFolderVersion.Add($"netcoreapp{v}");
                    }
                }

                return targetFrameworkShortFolderVersion;
            }
        }
    }

    public class SupportedAspNetCoreVersions : IEnumerable<object[]>
    {
        public IEnumerator<object[]> GetEnumerator() => Versions.Select(version => new object[] { version }).GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

        public static IEnumerable<string> Versions =>
            SupportedNetCoreAppVersions.Versions.Except(new List<string>() { "1.0", "1.1", "2.0" });
    }

    public class SupportedAspNetCoreAllVersions : IEnumerable<object[]>
    {
        public IEnumerator<object[]> GetEnumerator() => Versions.Select(version => new object[] { version }).GetEnumerator();
        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();

        public static IEnumerable<string> Versions =>
            SupportedAspNetCoreVersions.Versions.Where(v => new Version(v).Major < 3);
    }
}