Add module contracts and registry validation

internal/module/module_test.go

@@ -0,0 +1,84 @@
+package module
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+type testStanza struct {
+	Message string `json:"message"`
+	Count   int    `json:"count"`
+}
+
+func TestSnapshotPreservesOutputOrderAndJSON(t *testing.T) {
+	snapshot, err := NewSnapshot([]Output{
+		{ID: Metadata, StanzaName: "metadata", Value: testStanza{Message: "first", Count: 1}},
+		{ID: AlertDigest, StanzaName: "alert_digest", Value: testStanza{Message: "second", Count: 2}},
+	})
+	if err != nil {
+		t.Fatalf("NewSnapshot() error = %v", err)
+	}
+	if snapshot.SchemaVersion != SnapshotSchemaVersion {
+		t.Fatalf("SchemaVersion = %q, want %q", snapshot.SchemaVersion, SnapshotSchemaVersion)
+	}
+	if snapshot.Outputs[0].ID != Metadata || snapshot.Outputs[1].ID != AlertDigest {
+		t.Fatalf("Outputs order = %#v, want input order", snapshot.Outputs)
+	}
+
+	data, err := json.Marshal(snapshot)
+	if err != nil {
+		t.Fatalf("Marshal() error = %v", err)
+	}
+	got := string(data)
+	want := `{"schemaVersion":"weatherreporter.modules.v1","outputs":[{"id":"metadata","stanzaName":"metadata","value":{"message":"first","count":1}},{"id":"alert_digest","stanzaName":"alert_digest","value":{"message":"second","count":2}}]}`
+	if got != want {
+		t.Fatalf("json = %s, want %s", got, want)
+	}
+}
+
+func TestSnapshotRejectsDuplicateOutputs(t *testing.T) {
+	_, err := NewSnapshot([]Output{
+		{ID: Metadata, StanzaName: "metadata", Value: struct{}{}},
+		{ID: Metadata, StanzaName: "other_metadata", Value: struct{}{}},
+	})
+	if err == nil || !strings.Contains(err.Error(), `duplicate module output "metadata"`) {
+		t.Fatalf("duplicate module error = %v, want duplicate module output", err)
+	}
+
+	_, err = NewSnapshot([]Output{
+		{ID: Metadata, StanzaName: "metadata", Value: struct{}{}},
+		{ID: CurrentConditions, StanzaName: "metadata", Value: struct{}{}},
+	})
+	if err == nil || !strings.Contains(err.Error(), `duplicate stanza name "metadata"`) {
+		t.Fatalf("duplicate stanza error = %v, want duplicate stanza name", err)
+	}
+}
+
+func TestStanzaValueDecodesTypedOutput(t *testing.T) {
+	snapshot, err := NewSnapshot([]Output{
+		{ID: Metadata, StanzaName: "metadata", Value: testStanza{Message: "available", Count: 3}},
+	})
+	if err != nil {
+		t.Fatalf("NewSnapshot() error = %v", err)
+	}
+
+	value, found, err := StanzaValue[testStanza](snapshot, "metadata")
+	if err != nil {
+		t.Fatalf("StanzaValue() error = %v", err)
+	}
+	if !found {
+		t.Fatal("StanzaValue() found = false, want true")
+	}
+	if value.Message != "available" || value.Count != 3 {
+		t.Fatalf("StanzaValue() = %#v, want decoded stanza", value)
+	}
+
+	_, found, err = StanzaValue[testStanza](snapshot, "missing")
+	if err != nil {
+		t.Fatalf("StanzaValue(missing) error = %v", err)
+	}
+	if found {
+		t.Fatal("StanzaValue(missing) found = true, want false")
+	}
+}