Tests relying on .bashrc being loaded not working

Hi all.
First of all... great library, really like the simplicity of it.

We have a fairly rich docker container that makes heavy use of bash scripting to dynamically define env variables in the ~/,bashrc. After trying all kind of things for the last days I cannot get container structure tests to work in the context of the bashrc. Whatever I do, the env vars seem to be undefined.

Here's an example Dockerfile I wrote up:
```dockerfile
FROM debian:buster

RUN echo "export FOO=BAR" >> /root/.bashrc
RUN echo "echo 'bashrc loaded!'" >> ~/.bashrc

# this is strictly seen not necessary, but it forces the bashrc to be always loaded, not just in interactive mode and suppresses a related warning:
ENV BASH_ENV=/root/.bashrc
```

These are my example tests - they all fail.
The output indicates that the .bashrc is actually loaded, but the actual test seems to run separately under a different context - FOO seems never defined in the test context and the output of `$FOO` is always blank.

```yml
schemaVersion: 2.0.0

commandTests:
- name: "echo FOO"
command: echo
args: [ "$FOO" ]
expectedOutput: [ "BAR" ]
- name: "echo FOO using bash -c wrapper and enumerated args"
command: "bash"
args:
- -c
- "echo $FOO"
expectedOutput: [ "BAR" ]
- name: "echo FOO using bash -c wrapper and string array args"
command: "bash"
args: ["-c", "echo $FOO"]
expectedOutput: [ "BAR" ]
- name: "echo FOO using bash -c wrapper, pipe and source .bashrc"
command: "bash"
args:
- -c
- |
source ~/.bashrc &&
echo $FOO
expectedOutput: [ "BAR" ]
```
I also tried to specify a custom entry point using `setup: [["entrypoint.sh"]]` with the same result.
entrypoint.sh:
```bash
#!/bin/bash
source /root/.bashrc
```

Any help is greatly appreciated!
We already wrote fair a bit of non-bash tests, but cannot use this framework without proper bash support :(