Connecting to the local docker daemon using docker build (container in container)

I'm unable to connect to the local docker daemon when building a container using docker build on a Dockerfile.

1. Run: docker build -t myproj .
2. step inside Dockerfile: RUN dotnet test ./test.csproj
3. Code connects to client: unix:///var/run/docker.sock
4. Connection failed is returned

**Dockerfile:**

FROM microsoft/dotnet:2.2-sdk AS build-env
WORKDIR /app
COPY ./src ./
RUN dotnet restore ./myproj.Test/myproj.Test.csproj
RUN dotnet test ./myproj.Test/myproj.Test.csproj

**Connecting to the local daemon:**

` _client = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ?
new DockerClientConfiguration(new Uri("npipe://./pipe/docker_engine")).CreateClient() :
new DockerClientConfiguration(new Uri("unix:///var/run/docker.sock")).CreateClient();`