Update the README build and test section

AGENTS.md

@@ -45,6 +45,16 @@ dotnet run info MergeTwoLists
 dotnet run list
 ```
 
+## Updating .NET versions
+
+When you bump the .NET SDK or target framework, update these together:
+
+- `global.json`: the minimum SDK `version`.
+- `Directory.Build.props`: `TargetFramework`.
+- `LeetCode/Dockerfile`: the `sdk` and `runtime` image tags.
+- `README.md`: the minimum SDK, and the `dotnet --list-sdks` and `git --version` output under "Build and test".
+  Check for a newer git release at the same time.
+
 ## Architecture
 
 This is a LeetCode problem solutions repository with benchmarking capabilities, structured as follows:

README.md

@@ -8,21 +8,35 @@ After stumbling across the excellent [NeetCode](https://neetcode.io) website I'm
 
 ### Build and test
 
+Install the .NET 10 SDK, version 10.0.400 or later. `global.json` rolls forward to the newest feature band you have.
+
 ``` bash
 > dotnet --list-sdks
-10.0.103 [/usr/share/dotnet/sdk]
+10.0.402 [/usr/share/dotnet/sdk]
 
 > git --version
-git version 2.53.0
+git version 2.56.0
 
 > git clone https://github.com/si618/leetcode.git
 Cloning into 'leetcode'...
 
 > cd leetcode
 > dotnet build
-> dotnet test --no-restore
+> dotnet test
 ```
 
+Tests run on xUnit v3 with [Microsoft.Testing.Platform](https://learn.microsoft.com/dotnet/core/testing/microsoft-testing-platform-intro), and sit beside the solution they test.
+
+``` bash
+# Run a single test
+> dotnet test --project LeetCode.CSharp --filter-method "*TwoSumTest"
+
+# Write TRX results and Cobertura coverage to artifacts/test-results, as CI does
+> dotnet test --report-xunit-trx --results-directory artifacts/test-results --coverage --coverage-output-format cobertura
+```
+
+Build output goes to `artifacts/`, not to `bin/` and `obj/` in each project.
+
 ### Console application
 
 An interactive console application can run benchmarks and show problem information.