test(01-02): add failing test for layered compass config

- Cover six-level precedence, env mapping, .env, Set/Persist/Reload
- Require HasConfig merge before plugin Register
- Assert hello command observes overlay and plugin defaults

examples/hello/hello_test.go

@@ -9,14 +9,42 @@ import (
 	"testing"
 )
 
-func TestGreeterHelloPrintsAppName(t *testing.T) {
+func TestGreeterHelloPrintsLayeredConfig(t *testing.T) {
+	got := runHello(t, nil)
+	want := "name=hello-app posts_per_page=10 debug=false"
+	if got != want {
+		t.Fatalf("output = %q, want %q", got, want)
+	}
+}
+
+func TestGreeterHelloSeesDevelopmentOverlay(t *testing.T) {
+	got := runHello(t, map[string]string{"SUMMER_ENV": "development"})
+	want := "name=hello-dev posts_per_page=10 debug=true"
+	if got != want {
+		t.Fatalf("output = %q, want %q", got, want)
+	}
+}
+
+func TestGreeterHelloSeesEnvVarOverrideOfPluginDefault(t *testing.T) {
+	got := runHello(t, map[string]string{
+		"SUMMER_GOLEM15__HELLO__POSTS_PER_PAGE": "25",
+	})
+	want := "name=hello-app posts_per_page=25 debug=false"
+	if got != want {
+		t.Fatalf("output = %q, want %q", got, want)
+	}
+}
+
+func runHello(t *testing.T, env map[string]string) string {
+	t.Helper()
+	for k, v := range env {
+		t.Setenv(k, v)
+	}
 	var buf bytes.Buffer
 	if err := run([]string{"greeter:hello"}, &buf); err != nil {
 		t.Fatalf("greeter:hello: %v", err)
 	}
-	if got := strings.TrimSpace(buf.String()); got != "hello-app" {
-		t.Fatalf("output = %q, want %q", got, "hello-app")
-	}
+	return strings.TrimSpace(buf.String())
 }
 
 func TestBuiltBinaryGreeterHello(t *testing.T) {
@@ -33,8 +61,8 @@ func TestBuiltBinaryGreeterHello(t *testing.T) {
 	if err != nil {
 		t.Fatalf("bin/hello greeter:hello: %v\n%s", err, out)
 	}
-	if got := strings.TrimSpace(string(out)); got != "hello-app" {
-		t.Fatalf("output = %q, want %q", got, "hello-app")
+	if got := strings.TrimSpace(string(out)); got != "name=hello-app posts_per_page=10 debug=false" {
+		t.Fatalf("output = %q, want layered production config", got)
 	}
 }