Fix starting_containers test after release of Procfile CNB v3.0.0 (#…

…801)

Procfile CNB v3.0.0 was just released with an intentional change to the
way that `command` vs `args` are handled in the CNB process type
definition. (Before the `Procfile` file entry would be set as the
process `command`, but now it's set as `args`.)

That change improves the overall UX of running images that use the
Procfile CNB, but is breaking in some lesser used scenarios that
happened to be tested via the `starting_containers` test in this repo.

See:
- heroku/buildpacks-procfile#205 (comment)
- heroku/buildpacks-procfile@v2.0.2...v3.0.0#diff-782521a81713992d3a07e85975d367cfac60afc78583133551efcddc2026bd3eL19-R20

The tests have been updated to account for the new behaviour, and an
additional test added for the "overriding command only" scenario (that
wasn't possible to easily test before due to the way the Procfile CNB
was previously implemented).

Fixes #800.
GUS-W-15139634.

libcnb-test/tests/fixtures/procfile/Procfile

@@ -1,3 +1,2 @@
 web: python3 -u -m http.server ${PORT:+"${PORT}"}
 worker: echo 'this is the worker process!'
-echo-args: echo

libcnb-test/tests/integration_test.rs

@@ -37,7 +37,7 @@ fn build_other_buildpack() {
                 context.pack_stdout,
                 indoc! {"
                     [Discovering process types]
-                    Procfile declares types -> web, worker, echo-args
+                    Procfile declares types -> web, worker
                 "}
             );
         },
@@ -79,7 +79,7 @@ fn build_workspace_composite_buildpack() {
                     Buildpack B
                     
                     [Discovering process types]
-                    Procfile declares types -> web, worker, echo-args
+                    Procfile declares types -> web, worker
                 "}
             );
         },
@@ -103,7 +103,7 @@ fn build_multiple_buildpacks() {
                     Buildpack B
                     
                     [Discovering process types]
-                    Procfile declares types -> web, worker, echo-args
+                    Procfile declares types -> web, worker
                     Buildpack A
                 "}
             );
@@ -484,18 +484,31 @@ fn starting_containers() {
                 },
             );
 
-            // Overriding the default entrypoint, but using the default command.
+            // Overriding the entrypoint only.
             context.start_container(ContainerConfig::new().entrypoint("worker"), |container| {
                 let all_log_output = container.logs_wait();
                 assert_empty!(all_log_output.stderr);
                 assert_eq!(all_log_output.stdout, "this is the worker process!\n");
             });
 
+            // Overriding the command only.
+            context.start_container(
+                // The whole command has to be quoted since the Procfile CNB uses `bash -c`, which
+                // expects the next arg passed to it to be the entire bash command/script. See:
+                // https://github.com/heroku/procfile-cnb/pull/205#discussion_r1505866192
+                ContainerConfig::new().command(["echo 'this is a custom command!'"]),
+                |container| {
+                    let all_log_output = container.logs_wait();
+                    assert_empty!(all_log_output.stderr);
+                    assert_eq!(all_log_output.stdout, "this is a custom command!\n");
+                },
+            );
+
             // Overriding both the entrypoint and command.
             context.start_container(
                 ContainerConfig::new()
-                    .entrypoint("echo-args")
-                    .command(["$GREETING", "$DESIGNATION"])
+                    .entrypoint("launcher")
+                    .command(["echo", "$GREETING", "$DESIGNATION"])
                     .envs([("GREETING", "Hello"), ("DESIGNATION", "World")]),
                 |container| {
                     let all_log_output = container.logs_wait();