Publish current app and server

server/internal/recommend/explain_test.go

@@ -0,0 +1,136 @@
+package recommend
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+)
+
+func explainItem(t *testing.T, payload string) Item {
+	t.Helper()
+	items := Decode([]json.RawMessage{json.RawMessage(payload)})
+	if len(items) != 1 {
+		t.Fatalf("payload did not decode to one item: %s", payload)
+	}
+	return items[0]
+}
+
+func explainProfile(t *testing.T, history ...string) Profile {
+	t.Helper()
+	items := make([]Item, 0, len(history))
+	for _, payload := range history {
+		items = append(items, explainItem(t, payload))
+	}
+	return BuildProfile(items, nil)
+}
+
+const thrillerHistory = `{
+	"Id":"h1","Name":"Sicario","Type":"Movie","Genres":["Thriller","Crime"],
+	"Studios":[{"Name":"Lionsgate"}],
+	"People":[{"Name":"Denis Villeneuve","Type":"Director"},{"Name":"Emily Blunt","Type":"Actor"}]
+}`
+
+func TestWhyNamesTheGenreTheViewerActuallyWatches(t *testing.T) {
+	profile := explainProfile(t, thrillerHistory)
+	candidate := explainItem(t, `{
+		"Id":"c1","Name":"Prisoners","Type":"Movie","Genres":["Thriller"],
+		"People":[{"Name":"Denis Villeneuve","Type":"Director"}]
+	}`)
+
+	reasons := Why(profile, candidate, ReasonLimit)
+
+	if len(reasons) == 0 || reasons[0] != "Because you watch Thriller" {
+		t.Fatalf("expected the genre reason first, got %v", reasons)
+	}
+	if !strings.Contains(strings.Join(reasons, "|"), "Denis Villeneuve") {
+		t.Fatalf("expected the shared director to be named, got %v", reasons)
+	}
+}
+
+func TestWhyNeverClaimsAnAffinityThatIsNotThere(t *testing.T) {
+	profile := explainProfile(t, thrillerHistory)
+	candidate := explainItem(t, `{
+		"Id":"c2","Name":"Paddington","Type":"Movie","Genres":["Family"],
+		"CommunityRating":8.2,
+		"People":[{"Name":"Paul King","Type":"Director"}]
+	}`)
+
+	reasons := Why(profile, candidate, ReasonLimit)
+
+	for _, reason := range reasons {
+		if strings.HasPrefix(reason, "Because you watch") ||
+			strings.HasPrefix(reason, "You've watched") {
+			t.Fatalf("invented a taste the profile does not hold: %v", reasons)
+		}
+	}
+	if len(reasons) == 0 || reasons[0] != "Well rated (8.2)" {
+		t.Fatalf("expected the catalogue fact to carry the strip, got %v", reasons)
+	}
+}
+
+func TestWhyAlwaysSaysSomething(t *testing.T) {
+	candidate := explainItem(t, `{"Id":"c3","Name":"Unknown","Type":"Movie","Genres":["Drama"]}`)
+
+	reasons := Why(Profile{}, candidate, ReasonLimit)
+
+	if len(reasons) != 1 || reasons[0] != "Drama from your library" {
+		t.Fatalf("an empty profile should still explain the title, got %v", reasons)
+	}
+}
+
+func TestWhyIsCappedAndOrdered(t *testing.T) {
+	// A second, Thriller-only title so Thriller genuinely outweighs Crime — with one
+	// history item they tie and the alphabetical tie-break would decide it.
+	profile := explainProfile(t, thrillerHistory, `{
+		"Id":"h2","Name":"Nightcrawler","Type":"Movie","Genres":["Thriller"],
+		"Studios":[{"Name":"Lionsgate"}],
+		"People":[{"Name":"Emily Blunt","Type":"Actor"}]
+	}`)
+	candidate := explainItem(t, `{
+		"Id":"c4","Name":"Wind River","Type":"Movie","Genres":["Thriller","Crime"],
+		"Studios":[{"Name":"Lionsgate"}],"CommunityRating":9.1,"ProductionYear":2017,
+		"People":[{"Name":"Emily Blunt","Type":"Actor"}]
+	}`)
+
+	reasons := Why(profile, candidate, ReasonLimit)
+
+	if len(reasons) != ReasonLimit {
+		t.Fatalf("expected exactly %d reasons, got %v", ReasonLimit, reasons)
+	}
+	want := []string{
+		"Because you watch Thriller",
+		"You've watched Emily Blunt before",
+		"More from Lionsgate",
+	}
+	for i, reason := range want {
+		if reasons[i] != reason {
+			t.Fatalf("reason %d: want %q, got %q (%v)", i, reason, reasons[i], reasons)
+		}
+	}
+}
+
+func TestWhyIsStableAcrossCalls(t *testing.T) {
+	profile := explainProfile(t, thrillerHistory)
+	candidate := explainItem(t, `{
+		"Id":"c5","Name":"Hell or High Water","Type":"Movie","Genres":["Crime","Thriller"]
+	}`)
+
+	first := Why(profile, candidate, ReasonLimit)
+	for i := 0; i < 20; i++ {
+		if got := Why(profile, candidate, ReasonLimit); !equalStrings(first, got) {
+			t.Fatalf("reasons changed between calls: %v then %v", first, got)
+		}
+	}
+}
+
+func equalStrings(a, b []string) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}