petal/internal/llm/target_test.go

package llm

import (
	"strings"
	"testing"
)

// The prompt every account is on today, written out in full.
//
// Phase 28 gave the checkpoint a second framing for documents in the writer's
// own language, and the risk of that change is not that the new prompt is wrong
// — it is that the old one moved by a word while nobody was looking. Every user
// who exists is a Mandarin native writing English, so this string is the one
// Petal actually sends, all day. It is duplicated here on purpose: a golden
// copied from the constant it guards guards nothing.
const goldenEnglishCheckpointPrompt = `You are a warm, encouraging writing assistant helping someone who speaks English as a second language. Analyze the text below and identify up to 5 issues: grammar errors, unnatural phrasing, incorrect idiom usage, or unclear sentences that are common ESL patterns.

Be specific, friendly, and explain WHY each suggestion improves the writing.

Respond ONLY with valid JSON. No preamble, no markdown fences. Format:
{
  "suggestions": [
    {
      "original": "exact text from the document that needs fixing",
      "replacement": "corrected version",
      "explanation": "friendly one-sentence explanation",
      "type": "grammar|phrasing|idiom|clarity"
    }
  ]
}

If the writing looks good, return: {"suggestions": []}`

func TestEnglishDocumentPromptIsUnchanged(t *testing.T) {
	msgs := CheckpointMessages("I has two apple.", "", EnglishTarget(LangFor("zh")))
	if got := msgs[0].Content; got != goldenEnglishCheckpointPrompt {
		t.Fatalf("the English checkpoint prompt moved:\n--- got ---\n%s\n--- want ---\n%s", got, goldenEnglishCheckpointPrompt)
	}
	if msgs[1].Content != "I has two apple." {
		t.Fatalf("document text mangled: %q", msgs[1].Content)
	}

	// The tone clause still lands, in the same place it always did.
	toned := CheckpointMessages("x", "academic", EnglishTarget(LangFor("zh")))[0].Content
	if !strings.Contains(toned, "formal, academic, and objective") {
		t.Fatalf("English checkpoint lost its tone guidance:\n%s", toned)
	}
}

// A document in her own language gets a prompt that names that language, keeps
// the corrections inside it, and drops the framing that only makes sense when
// the thing being written is English.
func TestFlippedCheckpointPrompt(t *testing.T) {
	pt := LangFor("pt-PT")
	system := CheckpointMessages("Hoje foi um dia bom.", "casual", Target{Correct: pt, Explain: pt, Pair: pt})[0].Content

	if !strings.Contains(system, "European Portuguese") {
		t.Fatalf("flipped checkpoint doesn't name the language:\n%s", system)
	}
	if strings.Contains(system, "second language") || strings.Contains(system, "ESL") {
		t.Fatalf("flipped checkpoint kept the ESL framing:\n%s", system)
	}
	if !strings.Contains(system, "never translate it into English") {
		t.Fatalf("flipped checkpoint doesn't forbid translating:\n%s", system)
	}
	// The shared contract below the framing has to survive the split.
	for _, want := range []string{`"suggestions"`, `"replacement"`, "grammar|phrasing|idiom|clarity", "relaxed, friendly, and conversational"} {
		if !strings.Contains(system, want) {
			t.Fatalf("flipped checkpoint dropped %q:\n%s", want, system)
		}
	}
	if strings.Contains(system, "%!") {
		t.Fatalf("flipped checkpoint has a formatting error:\n%s", system)
	}
}

// The two decisions are separate arguments and must reach the prompt separately:
// corrections in the document's language, the explanation in the language she
// reads most easily. Only the zh pair can be travelled both ways today, so it is
// the only one that can prove they haven't been quietly collapsed into one.
func TestFlippedPromptsExplainInTheirOwnLanguage(t *testing.T) {
	zh := LangFor("zh")

	// Native Mandarin, practising English, writing Chinese: both halves Chinese.
	both := CheckpointMessages("今天天气很好。", "", Target{Correct: zh, Explain: zh, Pair: zh})[0].Content
	if strings.Count(both, "Simplified Chinese (Mandarin)") < 2 {
		t.Fatalf("expected corrections and explanations both in Chinese:\n%s", both)
	}
	if strings.Contains(both, "explanation"+`" in English`) {
		t.Fatalf("explanation language leaked to English:\n%s", both)
	}

	// Native English, learning Chinese, writing Chinese: Chinese corrections,
	// English explanations.
	split := CheckpointMessages("今天天气很好。", "", Target{Correct: zh, Explain: English, Pair: zh})[0].Content
	if !strings.Contains(split, `Write every "explanation" in English.`) {
		t.Fatalf("learner direction didn't get English explanations:\n%s", split)
	}
	if !strings.Contains(split, "writing in Simplified Chinese (Mandarin)") {
		t.Fatalf("learner direction lost its Chinese corrections:\n%s", split)
	}

	// Same for the voice pass, which had no language at all before this phase.
	voice := VoiceMessages("今天天气很好。", Target{Correct: zh, Explain: English, Pair: zh})[0].Content
	if !strings.Contains(voice, `Write every "explanation" in English.`) || !strings.Contains(voice, "Simplified Chinese") {
		t.Fatalf("flipped voice prompt got its languages wrong:\n%s", voice)
	}
	if strings.Contains(voice, "second language") {
		t.Fatalf("flipped voice prompt kept the ESL framing:\n%s", voice)
	}
	// An English document still gets exactly the voice prompt it always got.
	if got := VoiceMessages("x", EnglishTarget(zh))[0].Content; got != voiceSystemPrompt {
		t.Fatalf("English voice prompt moved:\n%s", got)
	}
}