Fix intermittent profile.d/ scripts test failure from extra trailing newline (#2102)

The `profile.d/` scripts test asserts on captured `run_multi` command output
using an exact match against a heredoc. The platform log stream that captures
the output occasionally appends an extra trailing newline, which intermittently
breaks these exact assertions.

For example:
https://github.com/heroku/heroku-buildpack-python/actions/runs/27144980449/job/80156740097?pr=2099#step:5:628

```
Failures:

  1) .profile.d/ scripts sets the required run-time env vars
     Failure/Error:
       expect(output).to eq(<<~OUTPUT)
         Python buildpack: Detected 512 MB available memory and 8 CPU cores.
         Python buildpack: Skipping automatic configuration of WEB_CONCURRENCY since it's already set.
         DYNO_RAM=512
         WEB_CONCURRENCY=999
       OUTPUT

       expected: "Python buildpack: Detected 512 MB available memory and 8 CPU cores.\nPython buildpack: Skipping auto...matic configuration of WEB_CONCURRENCY since it's already set.\nDYNO_RAM=512\nWEB_CONCURRENCY=999\n"
            got: "Python buildpack: Detected 512 MB available memory and 8 CPU cores.\nPython buildpack: Skipping auto...tic configuration of WEB_CONCURRENCY since it's already set.\nDYNO_RAM=512\nWEB_CONCURRENCY=999\n\n"

       (compared using ==)
     # ./spec/hatchet/profile_d_scripts_spec.rb:128:in 'block (4 levels) in <top (required)>'
     # ./vendor/bundle/ruby/4.0.0/gems/heroku_hatchet-8.0.6/lib/hatchet/app.rb:255:in 'block in Hatchet::App#run_multi'
```

Adds a `normalize_trailing_newlines` spec helper that collapses any trailing
newlines down to a single one, and applies it to the exact-match assertions in
the test. This absorbs the spurious trailing newline whilst still asserting on
the rest of the output exactly.

GUS-W-22900269.

Author: edmorley

spec/hatchet/profile_d_scripts_spec.rb

@@ -27,7 +27,7 @@
         'WEB_CONCURRENCY=this-should-be-preserved',
       ]
       app.run_multi(list_envs_cmd, heroku: { env: user_env_vars.join(';'), type: 'example-worker' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           DYNO_RAM=512
           FORWARDED_ALLOW_IPS=*
           GUNICORN_CMD_ARGS=this-should-be-preserved
@@ -48,7 +48,7 @@
       # Check WEB_CONCURRENCY support when using a Standard-1X dyno.
       # We set the process type to `web` so that we can test the web-dyno-only log output.
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'standard-1x', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 512 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 2 based on the available memory.
           DYNO_RAM=512
@@ -59,7 +59,7 @@
 
       # Standard-2X
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'standard-2x', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 1024 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 4 based on the available memory.
           DYNO_RAM=1024
@@ -70,7 +70,7 @@
 
       # Performance-M
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-m', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 2560 MB available memory and 2 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 5 based on the number of CPU cores.
           DYNO_RAM=2560
@@ -81,7 +81,7 @@
 
       # Performance-L
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-l', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 14336 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 17 based on the number of CPU cores.
           DYNO_RAM=14336
@@ -92,7 +92,7 @@
 
       # Performance-L-RAM
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-l-ram', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 30720 MB available memory and 4 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 9 based on the number of CPU cores.
           DYNO_RAM=30720
@@ -103,7 +103,7 @@
 
       # Performance-XL
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-xl', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 63488 MB available memory and 8 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 17 based on the number of CPU cores.
           DYNO_RAM=63488
@@ -114,7 +114,7 @@
 
       # Performance-2XL
       app.run_multi(list_concurrency_envs_cmd, heroku: { size: 'performance-2xl', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 129024 MB available memory and 16 CPU cores.
           Python buildpack: Defaulting WEB_CONCURRENCY to 33 based on the number of CPU cores.
           DYNO_RAM=129024
@@ -125,7 +125,7 @@
 
       # Check that WEB_CONCURRENCY is preserved if set, but that we still set DYNO_RAM.
       app.run_multi(list_concurrency_envs_cmd, heroku: { env: 'WEB_CONCURRENCY=999', type: 'web' }) do |output, _|
-        expect(output).to eq(<<~OUTPUT)
+        expect(normalize_trailing_newlines(output)).to eq(<<~OUTPUT)
           Python buildpack: Detected 512 MB available memory and 8 CPU cores.
           Python buildpack: Skipping automatic configuration of WEB_CONCURRENCY since it's already set.
           DYNO_RAM=512

spec/spec_helper.rb

@@ -62,6 +62,12 @@ def clean_output(output)
     .gsub(/\e\[[0-9;]+m/, '')
 end
 
+def normalize_trailing_newlines(output)
+  # The platform log stream that captures `run`/`run_multi` command output occasionally appends
+  # an extra trailing newline, which otherwise intermittently breaks exact output assertions.
+  output.sub(/\n+\z/, "\n")
+end
+
 def update_buildpacks(app, buildpacks)
   # Updates the list of buildpacks for an existing app, until Hatchet supports this natively:
   # https://github.com/heroku/hatchet/issues/166