test: fix example-buildpack

It wasn't used and didn't work without updating dependencies.

example-buildpack/Gemfile

@@ -2,4 +2,13 @@ source "https://rubygems.org"
 
 git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }
 
+# "rack" must be explicitly specified.
+# https://devcenter.heroku.com/articles/rack
+gem "rack"
+
+# While the doc above doesn't mention that, Ruby no longer have a HTTP server
+# by default. Use puma since webrick is not actively maintained.
+# https://bugs.ruby-lang.org/issues/17303
+gem "puma"
+
 gem "sinatra"

example-buildpack/Gemfile.lock

@@ -3,6 +3,9 @@ GEM
   specs:
     mustermann (2.0.2)
       ruby2_keywords (~> 0.0.1)
+    nio4r (2.7.4)
+    puma (6.5.0)
+      nio4r (~> 2.0)
     rack (2.2.8.1)
     rack-protection (2.2.3)
       rack
@@ -18,6 +21,8 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  puma
+  rack
   sinatra
 
 BUNDLED WITH

example-buildpack/fly.toml

@@ -4,7 +4,7 @@ app = "flyctl-example-buildpack"
 
 
 [build]
-  builder = "heroku/buildpacks:20"
+  builder = "heroku/builder:24"
 
 [deploy]
   release_command = "sh release.sh"

test/preflight/testlib/helpers.go

@@ -51,6 +51,11 @@ func otherRegionsFromEnv() []string {
 	}
 }
 
+func RepositoryRoot() string {
+	_, filename, _, _ := runtime.Caller(0)
+	return filepath.Join(path.Dir(filename), "../../..")
+}
+
 func currentRepoFlyctl() string {
 	_, filename, _, _ := runtime.Caller(0)
 	flyctlBin := path.Join(path.Dir(filename), "../../..", "bin", "flyctl")