run csharp tests under aarch64 emulator

kokoro/linux/aarch64/test_csharp_aarch64.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+set -ex
+
+# go to the repo root
+cd $(dirname $0)/../../..
+
+if [[ -t 0 ]]; then
+  DOCKER_TTY_ARGS="-it"
+else
+  # The input device on kokoro is not a TTY, so -it does not work.
+  DOCKER_TTY_ARGS=
+fi
+
+# First, build protobuf C# tests under x86_64 docker image
+# Tests are built "dotnet publish" because we want all the dependencies to the copied to the destination directory
+# (we want to avoid references to ~/.nuget that won't be available in the subsequent docker run)
+CSHARP_BUILD_COMMAND="dotnet publish -c Release -f net50 csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj"
+docker run $DOCKER_TTY_ARGS --rm --user "$(id -u):$(id -g)" -e "HOME=/home/fake-user" -e "DOTNET_CLI_TELEMETRY_OPTOUT=true" -e "DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true" -v "$(mktemp -d):/home/fake-user" -v "$(pwd)":/work -w /work mcr.microsoft.com/dotnet/sdk:5.0.202-buster-slim bash -c "$CSHARP_BUILD_COMAND"
+
+# Use an actual aarch64 docker image to run protobuf C# tests with an emulator. "dotnet vstest" allows
+# running tests from a pre-built project.
+# * mount the protobuf root as /work to be able to access the crosscompiled files
+# * to avoid running the process inside docker as root (which can pollute the workspace with files owned by root), we force
+#   running under current user's UID and GID. To be able to do that, we need to provide a home directory for the user
+#   otherwise the UID would be homeless under the docker container and pip install wouldn't work. For simplicity,
+#   we just run map the user's home to a throwaway temporary directory
+CSHARP_TEST_COMMAND="dotnet vstest csharp/src/Google.Protobuf.Test/bin/Release/net50/publish/Google.Protobuf.Test.dll"
+docker run $DOCKER_TTY_ARGS --rm --user "$(id -u):$(id -g)" -e "HOME=/home/fake-user" -e "DOTNET_CLI_TELEMETRY_OPTOUT=true" -e "DOTNET_SKIP_FIRST_TIME_EXPERIENCE=true" -v "$(mktemp -d):/home/fake-user" -v "$(pwd)":/work -w /work mcr.microsoft.com/dotnet/sdk:5.0.202-buster-slim-arm64v8 bash -c "$CSHARP_TEST_COMMAND"