Expand test matrix for conditional TargetFramework(s) fix (#3799)

- Add MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest fixture
  that reproduces the exact original issue shape (no unconditional
  TargetFramework/TargetFrameworks fallback element).
- Add case-insensitive configuration coverage (dEbUg/rElEaSe) for the
  conditional-frameworks fixture.
- Add a test asserting the correct default framework (first listed) is
  picked per configuration.
- Add a test asserting GetOutputDirectory resolves the output path for a
  specific requested TargetProfile (net45) inside conditional PropertyGroups.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

tests/Paket.Tests/Paket.Tests.fsproj

@@ -131,6 +131,7 @@
     <Compile Include="Simplifier\BasicScenarioSpecs.fs" />
     <TestAsset Include="ProjectFile\TestData\MicrosoftNetSdkWithTargetFrameworkAndOutputPath.csprojtest" />
     <TestAsset Include="ProjectFile\TestData\MicrosoftNetSdkWithConditionalTargetFrameworks.csprojtest" />
+    <TestAsset Include="ProjectFile\TestData\MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest" />
     <TestAsset Include="ProjectFile\TestData\EmptyFsharpGuid.fsprojtest" />
     <TestAsset Include="ProjectFile\TestData\EmptyVbGuid.vbprojtest" />
     <TestAsset Include="ProjectFile\TestData\EmptyPyGuid.pyprojtest" />

tests/Paket.Tests/ProjectFile/OutputSpecs.fs

@@ -105,13 +105,46 @@ let ``should detect output path for netsdk with outputPath and appendTargetFrame
 
 [<Test>]
 let ``should detect output path for netsdk with conditional target frameworks csproj file``
-        ([<Values("Debug", "Release")>] configuration) =
+        ([<Values("Debug", "Release", "dEbUg", "rElEaSe")>] configuration) =
     ensureDir ()
     let projectFile = ProjectFile.TryLoad("./ProjectFile/TestData/MicrosoftNetSdkWithConditionalTargetFrameworks.csprojtest").Value
     // Should not throw "Unable to find <configuration> output path node" (see issue #3799)
     let outPath = projectFile.GetOutputDirectory configuration "" None
     outPath |> shouldNotEqual ""
 
+[<Test>]
+let ``should detect output path for netsdk with only conditional target frameworks (no unconditional fallback) csproj file``
+        ([<Values("Debug", "Release")>] configuration) =
+    ensureDir ()
+    // Reproduces the exact shape from issue #3799: no unconditional TargetFramework/TargetFrameworks
+    // element exists at all, only Configuration-conditioned PropertyGroups.
+    let projectFile = ProjectFile.TryLoad("./ProjectFile/TestData/MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest").Value
+    let outPath = projectFile.GetOutputDirectory configuration "" None
+    outPath |> shouldNotEqual ""
+
+[<Test>]
+let ``should pick the conditional target frameworks matching the requested configuration for netsdk csproj file``
+        ([<Values("Debug", "Release")>] configuration) =
+    ensureDir ()
+    let projectFile = ProjectFile.TryLoad("./ProjectFile/TestData/MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest").Value
+    let outPath = projectFile.GetOutputDirectory configuration "" None
+    // Debug config only lists netstandard2.0;net45, Release additionally lists net47;
+    // the first framework in each list is netstandard2.0, and it should be selected as the default.
+    let expected = (System.IO.Path.Combine(@"bin", configuration, "netstandard2.0") |> normalizePath)
+    outPath.ToLowerInvariant() |> shouldEqual (expected.ToLowerInvariant())
+
+[<Test>]
+let ``should detect output path for a specific target profile in a conditional target frameworks csproj file``
+        ([<Values("Debug", "Release")>] configuration) =
+    ensureDir ()
+    let projectFile = ProjectFile.TryLoad("./ProjectFile/TestData/MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest").Value
+    let targetProfile =
+        FrameworkDetection.internalExtract "net45"
+        |> Option.map TargetProfile.SinglePlatform
+    let outPath = projectFile.GetOutputDirectory configuration "" targetProfile
+    let expected = (System.IO.Path.Combine(@"bin", configuration, "net45") |> normalizePath)
+    outPath.ToLowerInvariant() |> shouldEqual (expected.ToLowerInvariant())
+
 [<Test>]
 let ``should detect framework profile for ProjectWithConditions file`` () =
     ensureDir ()

tests/Paket.Tests/ProjectFile/TestData/MicrosoftNetSdkWithConditionalTargetFrameworksOnly.csprojtest

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup Condition="'$(Configuration)'=='Debug'">
+    <TargetFrameworks>netstandard2.0;net45</TargetFrameworks>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(Configuration)'=='Release'">
+    <TargetFrameworks>netstandard2.0;net45;net47</TargetFrameworks>
+  </PropertyGroup>
+</Project>