undefined method `k8sobjects'

[sirhopcount]

I'm trying to build a docker container to run inspec-k8s but when executing Inspec I get the following error for all defined resources:

inspec exec mgmt -t k8s://

Profile: InSpec K8s Profile
Version: 0.1.0
Target:  kubernetes://XXXXXXX:XXXX

  ×  k8s-1.0: Validate built-in namespaces
     ×  Control Source Code Error /srv/mgmt/controls/basics.rb:3 
     undefined method `k8sobject' for #<Inspec::Rule:0x00000000070f0788>
...

Profile Summary: 0 successful controls, 7 control failures, 0 controls skipped
Test Summary: 0 successful, 7 failures, 0 skipped

I'm using the following versions:

• inspec: 4.56.20
• inspec-bin: 4.56.20
• train-kubernetes: 0.1.10
• k8s-ruby: 0.10.5

I ensured = has been removed from plugins.json:

# cat ~/.inspec/plugins.json
{
  "plugins_config_version": "1.0.0",
  "plugins": [
    {
      "name": "train-kubernetes",
      "version": "0.1.10"
    }
  ]

I've ensured only one version of excon is installed:

# gem list |grep excon
excon (0.92.2)
faraday-excon (1.1.0)

Inspect detect:

# inspec detect -t k8s://

== Platform Details

Name:      k8s
Families:  cloud, api
Release:   0.1.10

The Dockerfile in question:

FROM chef/inspec:4.56.20

## Install dependencies
RUN apt-get update && \
    apt install -y build-essential ruby-dev coreutils bash git

## Fix path issue.
RUN ln -s /bin/mkdir /usr/bin/mkdir

## Install kubernetes plugin
RUN gem install inspec-bin -v 4.56.20 --no-document --quiet
RUN gem install train-kubernetes

## Accept license
ENV CHEF_LICENSE=accept
RUN inspec plugin install train-kubernetes

## Fix version issue
RUN sed -ie 's#"= 0#"0#g' /root/.inspec/plugins.json

## Volume and workdir
VOLUME ["/srv"]
WORKDIR /srv

## Set entrypoint and command.
ENTRYPOINT ["inspec"]
CMD ["help"]

The tests in question:

control "k8s-1.0" do
  impact 0.2
  title "Validate built-in namespaces"
  desc "The kube-system, kube-public and default namespaces should exist"

  describe k8sobject(api: 'v1', type: 'namespaces', name: 'default') do
    it { should exist }
  end
  describe k8sobject(api: 'v1', type: 'namespaces', name: 'kube-system') do
    it { should exist }
  end
  describe k8sobject(api: 'v1', type: 'namespaces', name: 'kube-public') do
    it { should exist }
  end
end

I used version 4.56.20 because that is the latest version I could find for version 4.x for both inspec and inspec-bin. I also tried with version 5.18.15 of Inspec but that wouldn't even run.

If you need any more information please let me know.