add article

_config.yml

@@ -15,7 +15,7 @@ nav_external_links:
   # - title: Guiding principles
   #   url: "#guiding-principles"
   #   hide_icon: true
-  - title: Describe what you are testing
+  - title: Describe what you're testing
     url: "#describe"
     hide_icon: true
   - title: Use contexts
@@ -66,6 +66,9 @@ nav_external_links:
   - title: Stub HTTP requests
     url: "#stub-http-requests"
     hide_icon: true
+  - title: Stub environment variables
+    url: "#stub-environment-variables"
+    hide_icon: true
   - title: Create only the data you need
     url: "#create-only-the-data-you-need"
     hide_icon: true

_includes/nav_footer_custom.html

@@ -0,0 +1 @@
+ 

_includes/stub_env_vars.html

@@ -0,0 +1,55 @@
+<article>
+  <h2 id="stub-environment-variables">
+    <a href="#stub-environment-variables">
+      Stub environment variables
+    </a>
+  </h2>
+
+  <p>Stub environment variables your code requires so your tests become more self-contained, the <a href="https://rubygems.org/gems/stub_env" target="_blank">stub_env</a> gem might help you with that.</p>
+
+  <div class="example">
+{% highlight ruby %}
+def notify_sales_team
+  mail(
+    to: ENV['SALES_TEAM_EMAIL'],
+    subject: 'New sale'
+  )
+end
+{% endhighlight %}
+  </div>
+
+  <div class="bad">
+{% highlight ruby %}
+describe '#notify_sales_team' do
+  it 'prepares the email' do
+    subject = described_class.notify_sales_team
+
+    expect(subject.to).to eq(['[email protected]'])
+    expect(subject.subject).to eq('New sale')
+  end
+end
+{% endhighlight %}
+  </div>
+
+  <div class="bad">
+{% highlight ruby %}
+# .env.test
+SALES_TEAM_EMAIL='[email protected]'
+{% endhighlight %}
+  </div>
+
+  <div class="good">
+{% highlight ruby %}
+describe '#notify_sales_team' do
+  it 'prepares the email' do
+    stub_env('SALES_TEAM_EMAIL', '[email protected]')
+
+    subject = described_class.notify_sales_team
+
+    expect(subject.to).to eq(['[email protected]'])
+    expect(subject.subject).to eq('New sale')
+  end
+end
+{% endhighlight %}
+  </div>
+</article>

index.html

@@ -43,4 +43,5 @@ <h2>
 {% include dont_use_shared_examples.html %}
 {% include mock_external_dependencies.html %}
 {% include stub_http_requests.html %}
+{% include stub_env_vars.html %}
 {% include create_only_the_data_you_need.html %}