Add a test that covers a situation where one secret path doesn't exist

acceptance/features/fetching_secrets.feature

@@ -14,3 +14,14 @@ Feature: fetching secrets
 		And a secret "very/secret/db-password" with "notSoSecret"
 		When I successfully run `summon -p ./provider env`
 		Then the output should contain "DB_PASSWORD=notSoSecret"
+
+	Scenario: Fetching a database username and non existent password
+		Given a file named "secrets.yml" with:
+			"""
+			DB_USERNAME: !var very/secret/db-username
+			DB_PASSWORD: !var very/secret/db-password-non-existent
+			"""
+		And a secret "very/secret/db-username" with "secretUsername"
+		And a non-existent secret "very/secret/db-password-non-existent"
+		When I run `summon -p ./provider env`
+		Then the output should contain "Error fetching variable DB_PASSWORD"

acceptance/features/step_definitions/secret_steps.rb

@@ -35,3 +35,15 @@
 			"""
 	}
 end
+
+Given(/^a non-existent secret "([^"]*)"$/) do |name|
+	steps %{
+		Given I append to "provider" with:
+			"""
+			if [ "$1" == "#{name}" ]; then
+        	    echo "Error fetching variable #{name}" >&2
+        	    exit 1
+			fi
+			"""
+	}
+end