Use Dir.pwd instead of ENV['PWD'] in Capistrano integration (#848)

* Use Dir.pwd instead of ENV['PWD']

I'm using a pretty different setup for my Deploy with Capistrano, which
includes deploying from a dev container in rootless podman, using the
Ruby on Whales guide, with some changes.

I don't know exactly why it happens, but when deploying ENV["PWD"]
returns nil. I tinkered a little and it seems that Dir.pwd is more
reliable.

* Use Dir.chdir to mock directory in Capistrano spec

Instead of mocking the `Dir.pwd` method, switch the current directory to
what the test expects it to be. This doesn't interfere with our internal
test system.

Co-authored-by: Tomás Coêlho <tomascoelho6@gmail.com>
Co-authored-by: Tom de Bruijn <tom@tomdebruijn.com>

.changesets/use-dir-pwd-for-capistrano-3-current-directory.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "fix"
+---
+
+Use `Dir.pwd` to determine the current directory in the Capistrano 3 integration. It previously relied on `ENV["pwd"]` which returned `nil` in some scenarios.

lib/appsignal/integrations/capistrano/appsignal.cap

@@ -5,7 +5,7 @@ namespace :appsignal do
     revision = fetch(:appsignal_revision, fetch(:current_revision))
 
     appsignal_config = Appsignal::Config.new(
-      ENV["PWD"],
+      Dir.pwd,
       appsignal_env,
       {},
       Logger.new(StringIO.new)

spec/lib/appsignal/capistrano3_spec.rb

@@ -42,7 +42,11 @@ def run
     describe "appsignal:deploy task" do
       before do
         ENV["USER"] = "batman"
-        ENV["PWD"] = project_fixture_path
+      end
+      around do |example|
+        Dir.chdir project_fixture_path do
+          example.run
+        end
       end
 
       context "config" do