inspec/docs/style.md

# InSpec profile style guide

This is a set of recommended InSpec rules you should use when writing controls.

## Control files

### 1. All controls should be located in the "controls" directory and end in ".rb"

Reason: Most syntax highlighters will render InSpec files correctly across a wide list of tools.

Avoid: `controls/ssh_config`
Use: `controls/ssh_config.rb`

Avoid: `controls/ssh/config.rb`
Use: `controls/ssh_config.rb`

### 2. Avoid using "controls" or "control" in the name of your control files

Reason: Using `controls` in the filename again duplicates it and creates unnecessary clutter when reading it. Keep the names short and concise.

Avoid: `controls/ssh_controls.rb`
Use: `controls/ssh.rb`


## Code style

### 3. Avoid unnecessary parentheses in matchers

Adding additional parentheses is not required and provides more readability if it is not used:

Avoid: `it { should eq(value) }`
Use: `it { should eq value }`

The exception are matchers that require additional arguments or named arguments.


## Controls

### 4. Do not wrap controls in conditional statements

Reason: This will create dynamic profiles whose controls depend on the execution. The problem here is that we cannot render the profile or provide its information before scanning a system. We want to be able to inform users of the contents of their profiles before they run them. It is valid to skip controls that are not necessary for a system, as long as you do it via `only_if` conditions. Ruby's internal conditionals will hide parts of the profile to static analysis and should thus be avoided.

Avoid:
```ruby
if package('..').installed?
  control "package-test1" do
    ..
  end
end
```

Use:
```ruby
control "package-test1" do
  only_if { package('..').installed? }
end
```

Avoid:
```ruby
case inspec.platform.name
when /centos/
  include_controls 'centos-profile'
...
```

Use: The `supports` attribute in `inspec.yml` files of the profile you want to include:

```ruby
supports:
- platform-name: centos
```

Now whenever you run the base profile you can just `include_controls 'centos-profile'`.
It will only run the included profiles is the platform matches the supported platform.


### 5. Do not include dynamic elements in the control IDs

Reason: Control IDs are used to map test results to the tests and profiles. Dynamic control IDs make it impossible to map results back, since the identifier which connects tests and results may change in the process.

Avoid:
```ruby
control "test-file-#{name}" do
  ..
end
```

Use:
```ruby
control "test-all-files" do
  ..
end
```

Sometimes you may create controls from a static list of elements. If this list stays the same no matter what system is scanned, it may be ok to do so and use it as a generator for static controls.


### 6. Avoid Ruby system calls

Reason: Ruby code is executed on the system that runs InSpec. This allows
InSpec to work without Ruby and rubygems being required on remote
targets (servers or containers). System calls are often used to interact with
the local OS or remote endpoints from a local installation.
InSpec tests, however, are designed to be universally executable on all
types of runtimes, including local and remote execution. We want to give
users the ability to take an OS profile and execute it remotely or locally.

**Avoid shelling out**

Avoid: `` `ls``\`
Avoid: `system("ls")`
Avoid: `IO.popen("ls")`
Use: `command("ls")` or `powershell("..")`

Ruby's command executors will only run localy. Imagine a test like this:

```ruby
describe `whoami` do
  it { should eq "bob\n" }
end
```

If you run this test on your local system and happen to be using Bob's account
it will succeed. But if you were to run it against `--target alice@remote-host.com`
it will still report that the user is bob instead of alice.

Instead, do this:

```ruby
describe command('whoami') do
  its('stdout') { should eq "bob\n" }
end
```

If the profile is pointed to a remote endpoint using the `command` resource
will run it on the remote OS.

**Avoid Ruby IO on files**

Avoid: `File.new("filename").read`
Avoid: `File.read("filename")`
Avoid: `IO.read("filename")`
Use: `file("filename")`

Similar to the command interactions these files will only be read localy
with Ruby's internal calls. If you run this test against a remote target it won't
read the file from the remote endpoint, but from the local OS instead.
Use the `file` resource to read files on the target system.

In general, try to avoid Ruby's IO calls from within InSpec controls and
use InSpec resources instead.


### 7. Avoid Ruby gem dependencies in controls

In addition to avoiding system-level gems and modules you should also limit
the use of external dependencies to resource packs or plugins. Gems need to be
resolved, installed, vendored, and protected from conflicts. We aim to avoid
exposing this complexity to users of InSpec, to make it a great tool even if
you are not a developer.

Developers may still use external gem dependencies but should vendor it
with their plugins or resource packs.


### 8. Avoid debugging calls (in production)

Reason: One of the best way to develop and explore tests is the interactive debugging shell `pry` (see the section on "Interactive Debugging with Pry" at the end of this page). However, after you finish your profile make sure you have no interactive statements included anymore. Sometimes interactive calls are hidden behind conditionals (`if` statements) that are harder to reach. These calls can easily cause trouble when an automated profiles runs into an interactive `pry` call that stops the execution and waits for user input.

Avoid: `binding.pry` in production profiles
Use: Use debugging calls during development only

Also you may find it helpful to use the inspec logging interface:

```ruby
Inspec::Log.info('Hi')
```