testable

Author: Nigusu-Allehu

src/NuGet.Core/NuGet.Common/NuGetFeatureFlags.cs

@@ -11,18 +11,20 @@ public static class NuGetFeatureFlags
         internal const string UsesNSJDeserializationSwitchName = "NuGet.UsesNSJDeserialization";
         internal const string UsesNSJDeserializationEnvVar = "NUGET_USES_NSJ_DESERIALIZATION";
 
-        /// <summary>
-        /// <see langword="true"/> to use Newtonsoft.Json (default); <see langword="false"/> to use System.Text.Json.
-        /// Override via AppContext switch <c>NuGet.UsesNSJDeserialization</c> or env var <c>NUGET_USES_NSJ_DESERIALIZATION</c>.
-        /// </summary>
+        private static readonly Lazy<bool> _isNSJDeserializationEnabledByEnvironment =
+            new Lazy<bool>(() => IsNSJDeserializationEnabledByEnvironment(EnvironmentVariableWrapper.Instance));
+
+        /// <summary>Feature switch for NSJ deserialization. Defaults to <see langword="true"/>.</summary>
         [FeatureSwitchDefinition(UsesNSJDeserializationSwitchName)]
-        public static bool UsesNSJDeserialization { get; } = GetSwitch(EnvironmentVariableWrapper.Instance);
+        public static bool NSJDeserializationFeatureSwitch { get; } =
+            !AppContext.TryGetSwitch(UsesNSJDeserializationSwitchName, out bool value) || value;
 
-        internal static bool GetSwitch(IEnvironmentVariableReader env)
+        /// <summary>Returns <see langword="false"/> when env var <c>NUGET_USES_NSJ_DESERIALIZATION</c> is <c>false</c>.</summary>
+        public static bool IsNSJDeserializationEnabledByEnvironment(IEnvironmentVariableReader? env = null)
         {
-            if (AppContext.TryGetSwitch(UsesNSJDeserializationSwitchName, out bool switchValue))
+            if (env is null)
             {
-                return switchValue;
+                return _isNSJDeserializationEnabledByEnvironment.Value;
             }
 
             string? envValue = env.GetEnvironmentVariable(UsesNSJDeserializationEnvVar);

src/NuGet.Core/NuGet.Common/PublicAPI.Unshipped.txt

@@ -1,3 +1,4 @@
 #nullable enable
 NuGet.Common.NuGetFeatureFlags
-static NuGet.Common.NuGetFeatureFlags.UsesNSJDeserialization.get -> bool
+static NuGet.Common.NuGetFeatureFlags.IsNSJDeserializationEnabledByEnvironment(NuGet.Common.IEnvironmentVariableReader? env = null) -> bool
+static NuGet.Common.NuGetFeatureFlags.NSJDeserializationFeatureSwitch.get -> bool

test/NuGet.Core.Tests/NuGet.Common.Test/NuGetFeatureFlagsTests.cs

@@ -10,25 +10,27 @@ namespace NuGet.Common.Test
     public class NuGetFeatureFlagsTests
     {
         [Fact]
-        public void GetSwitch_WhenEnvVarNotSet_ReturnsTrue()
+        public void NSJDeserializationFeatureSwitch_Default_ReturnsTrue()
         {
-            bool result = NuGetFeatureFlags.GetSwitch(TestEnvironmentVariableReader.EmptyInstance);
+            Assert.True(NuGetFeatureFlags.NSJDeserializationFeatureSwitch);
+        }
 
-            Assert.True(result);
+        [Fact]
+        public void IsNSJDeserializationEnabledByEnvironment_WhenEnvVarNotSet_ReturnsTrue()
+        {
+            Assert.True(NuGetFeatureFlags.IsNSJDeserializationEnabledByEnvironment(TestEnvironmentVariableReader.EmptyInstance));
         }
 
         [Theory]
         [InlineData("false")]
         [InlineData("False")]
         [InlineData("FALSE")]
-        public void GetSwitch_WhenEnvVarSetToFalse_ReturnsFalse(string value)
+        public void IsNSJDeserializationEnabledByEnvironment_WhenEnvVarSetToFalse_ReturnsFalse(string value)
         {
             var env = new TestEnvironmentVariableReader(
                 new Dictionary<string, string> { [NuGetFeatureFlags.UsesNSJDeserializationEnvVar] = value });
 
-            bool result = NuGetFeatureFlags.GetSwitch(env);
-
-            Assert.False(result);
+            Assert.False(NuGetFeatureFlags.IsNSJDeserializationEnabledByEnvironment(env));
         }
 
         [Theory]
@@ -37,14 +39,12 @@ public void GetSwitch_WhenEnvVarSetToFalse_ReturnsFalse(string value)
         [InlineData("0")]
         [InlineData("1")]
         [InlineData("anything")]
-        public void GetSwitch_WhenEnvVarSetToTrueOrUnrecognized_ReturnsTrue(string value)
+        public void IsNSJDeserializationEnabledByEnvironment_WhenEnvVarSetToTrueOrUnrecognized_ReturnsTrue(string value)
         {
             var env = new TestEnvironmentVariableReader(
                 new Dictionary<string, string> { [NuGetFeatureFlags.UsesNSJDeserializationEnvVar] = value });
 
-            bool result = NuGetFeatureFlags.GetSwitch(env);
-
-            Assert.True(result);
+            Assert.True(NuGetFeatureFlags.IsNSJDeserializationEnabledByEnvironment(env));
         }
     }
 }