OSS-905 [csharp] Add tests for all supported versions (#168)

Author: shestakovg

.circleci/config.yml

@@ -9,7 +9,7 @@ executors:
         enum: ["stable", "nightly"]
     resource_class: large
     docker:
-      - image: mcr.microsoft.com/dotnet/core/sdk:3.1
+      - image: mcr.microsoft.com/dotnet/sdk
 
       - image: gcr.io/faunadb-cloud/faunadb/enterprise/<<parameters.version>>:latest
         name: core
@@ -36,15 +36,43 @@ commands:
             while ! $(curl --output /dev/null --silent --fail --max-time 1 http://core:8443/ping); do sleep 1; done
 
       - run:
-          name: Run Tests
+          name: Run Tests 3.1
           command: |
+            wget https://packages.microsoft.com/config/debian/10/packages-microsoft-prod.deb -O packages-microsoft-prod.deb
+            dpkg -i packages-microsoft-prod.deb
+            rm packages-microsoft-prod.deb
+            apt-get update; \
+            apt-get install -y apt-transport-https && \
+            apt-get update && \
+            apt-get install -y dotnet-sdk-3.1
             dotnet --info
-            mkdir results
+            mkdir TestResults
             dotnet restore
-            dotnet test --framework netcoreapp3.1 --logger "junit;LogFilePath=./results/results.xml" FaunaDB.Client.Test
-
+            dotnet test --framework netcoreapp3.1 --logger "junit;LogFilePath=./TestResults/results31.xml" FaunaDB.Client.Test
+      
+      - run:
+          name: Run Tests 5.0
+          command: |
+            dotnet --info
+            dotnet restore
+            dotnet test --framework net5.0 --logger "junit;LogFilePath=./TestResults/results50.xml" FaunaDB.Client.Test
+            
+      - run:
+          name: Run Tests 45
+          command: |
+            apt update
+            apt -y install dirmngr gnupg apt-transport-https ca-certificates
+            apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
+            sh -c 'echo "deb https://download.mono-project.com/repo/debian stable-buster main" > /etc/apt/sources.list.d/mono-official-stable.list'
+            apt update
+            apt-get -y install mono-devel
+            mono --version
+            dotnet --info
+            dotnet restore
+            dotnet test --framework net45 --logger "trx;LogFileName=results45.xml" FaunaDB.Client.Test
+            
       - store_test_results:
-          path: FaunaDB.Client.Test/results/
+          path: FaunaDB.Client.Test/TestResults/
 
 jobs:
   core-stable: