Add more tests

A legacy Django version (1.18, which is EOL) is now tested,
as well as ensuring that env vars are passed to manage.py.

src/django.rs

@@ -100,7 +100,10 @@ mod tests {
 
     #[test]
     fn has_management_script_django_project() {
-        assert!(has_management_script(Path::new("tests/fixtures/django_collectstatic")).unwrap());
+        assert!(has_management_script(Path::new(
+            "tests/fixtures/django_staticfiles_latest_django"
+        ))
+        .unwrap());
     }
 
     #[test]

tests/django_test.rs

@@ -6,9 +6,11 @@ use libcnb_test::{assert_contains, assert_empty, BuildConfig, PackResult, TestRu
 // them when the Django app is nested inside a subdirectory (such as in backend+frontend monorepos).
 #[test]
 #[ignore = "integration test"]
-fn django_collectstatic() {
+fn django_staticfiles_latest_django() {
     TestRunner::default().build(
-        BuildConfig::new(builder(), "tests/fixtures/django_collectstatic"),
+        BuildConfig::new(builder(), "tests/fixtures/django_staticfiles_latest_django")
+            // Tests that env vars are passed to the 'manage.py' script invocations.
+            .env("EXPECTED_ENV_VAR", "1"),
         |context| {
             assert_empty!(context.pack_stderr);
             assert_contains!(
@@ -24,6 +26,31 @@ fn django_collectstatic() {
     );
 }
 
+// This tests the oldest Django version that works on Python 3.9 (which is the
+// oldest Python that is available on all of our supported builders).
+#[test]
+#[ignore = "integration test"]
+fn django_staticfiles_legacy_django() {
+    TestRunner::default().build(
+        BuildConfig::new(builder(), "tests/fixtures/django_staticfiles_legacy_django"),
+        |context| {
+            assert_empty!(context.pack_stderr);
+            assert_contains!(
+                context.pack_stdout,
+                indoc! {"
+                    Successfully installed Django-1.8.19
+                    
+                    [Generating Django static files]
+                    Running 'manage.py collectstatic'
+                    Linking '/workspace/testapp/static/robots.txt'
+                    
+                    1 static file symlinked to '/workspace/staticfiles'.
+                "}
+            );
+        },
+    );
+}
+
 #[test]
 #[ignore = "integration test"]
 fn django_no_manage_py() {

tests/fixtures/django_staticfiles_latest_django/backend/testproject/settings.py

@@ -0,0 +1,15 @@
+import os
+from pathlib import Path
+
+BASE_DIR = Path(__file__).resolve().parent.parent
+
+INSTALLED_APPS = [
+    "django.contrib.staticfiles",
+    "testapp",
+]
+
+STATIC_ROOT = BASE_DIR / "staticfiles"
+STATIC_URL = "static/"
+
+# Tests that app env vars are passed to the 'manage.py' script invocations.
+assert "EXPECTED_ENV_VAR" in os.environ

tests/fixtures/django_staticfiles_legacy_django/manage.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python
+import os
+import sys
+
+if __name__ == "__main__":
+    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "testproject.settings")
+
+    from django.core.management import execute_from_command_line
+
+    execute_from_command_line(sys.argv)

tests/fixtures/django_staticfiles_legacy_django/requirements.txt

@@ -0,0 +1,3 @@
+# This is the oldest Django version that works on Python 3.9 (which is the
+# oldest Python that is available on all of our supported builders).
+Django==1.8.19

tests/fixtures/django_staticfiles_legacy_django/runtime.txt

@@ -0,0 +1 @@
+python-3.9.18

tests/fixtures/django_collectstatic/backend/testproject/settings.py → tests/fixtures/django_staticfiles_legacy_django/testproject/settings.py

@@ -9,3 +9,5 @@
 
 STATIC_ROOT = BASE_DIR / "staticfiles"
 STATIC_URL = "static/"
+
+SECRET_KEY = "example"

tests/fixtures/pip_basic/manage.py

@@ -1,2 +1,2 @@
 # Tests that manage.py alone doesn't trigger Django collectstatic.
-raise Exception("This is not a Django app")
+raise RuntimeError("This is not a Django app, so manage.py should not be run!")