test: add tests for merchant dashboard metrics and fix invoice template location

Move invoice PDF template from app/templates/invoices/ to
app/modules/orders/templates/invoices/ where InvoicePDFService expects it.
Expand invoice PDF tests to validate template path and existence.

Add unit tests for get_merchant_metrics() in tenancy, billing, and
customer metrics providers. Add unit tests for StatsAggregatorService
merchant methods. Add integration tests for the merchant dashboard
stats endpoint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/billing/tests/unit/test_billing_metrics.py

@@ -0,0 +1,149 @@
+# app/modules/billing/tests/unit/test_billing_metrics.py
+"""Unit tests for BillingMetricsProvider.get_merchant_metrics."""
+
+import uuid
+from datetime import UTC, datetime, timedelta
+
+import pytest
+
+from app.modules.billing.models import (
+    MerchantSubscription,
+    SubscriptionStatus,
+    SubscriptionTier,
+)
+from app.modules.billing.services.billing_metrics import BillingMetricsProvider
+from app.modules.tenancy.models import Merchant, Platform, User
+
+
+@pytest.fixture
+def billing_platform(db):
+    """Create a platform for billing metrics tests."""
+    platform = Platform(
+        code=f"bm_{uuid.uuid4().hex[:8]}",
+        name="Billing Metrics Platform",
+        is_active=True,
+    )
+    db.add(platform)
+    db.commit()
+    db.refresh(platform)
+    return platform
+
+
+@pytest.fixture
+def billing_merchant(db):
+    """Create a merchant for billing metrics tests."""
+    from middleware.auth import AuthManager
+
+    auth = AuthManager()
+    user = User(
+        email=f"billowner_{uuid.uuid4().hex[:8]}@test.com",
+        username=f"billowner_{uuid.uuid4().hex[:8]}",
+        hashed_password=auth.hash_password("pass123"),
+        role="merchant_owner",
+        is_active=True,
+    )
+    db.add(user)
+    db.flush()
+
+    merchant = Merchant(
+        name="Billing Metrics Merchant",
+        owner_user_id=user.id,
+        contact_email=user.email,
+        is_active=True,
+        is_verified=True,
+    )
+    db.add(merchant)
+    db.commit()
+    db.refresh(merchant)
+    return merchant
+
+
+@pytest.fixture
+def billing_tier(db, billing_platform):
+    """Create a subscription tier."""
+    tier = SubscriptionTier(
+        code="professional",
+        name="Professional",
+        description="Pro tier",
+        price_monthly_cents=2900,
+        price_annual_cents=29000,
+        display_order=1,
+        is_active=True,
+        is_public=True,
+        platform_id=billing_platform.id,
+    )
+    db.add(tier)
+    db.commit()
+    db.refresh(tier)
+    return tier
+
+
+@pytest.fixture
+def billing_extra_platforms(db):
+    """Create additional platforms for multiple subscriptions (unique constraint: merchant+platform)."""
+    platforms = []
+    for i in range(2):
+        p = Platform(
+            code=f"bm_extra_{uuid.uuid4().hex[:8]}",
+            name=f"Extra Platform {i}",
+            is_active=True,
+        )
+        db.add(p)
+        platforms.append(p)
+    db.commit()
+    for p in platforms:
+        db.refresh(p)
+    return platforms
+
+
+@pytest.fixture
+def billing_subscriptions(db, billing_merchant, billing_platform, billing_tier, billing_extra_platforms):
+    """Create subscriptions: 1 active, 1 trial, 1 cancelled (each on a different platform)."""
+    platforms = [billing_platform, billing_extra_platforms[0], billing_extra_platforms[1]]
+    subs = []
+    for status, platform in zip(
+        [SubscriptionStatus.ACTIVE, SubscriptionStatus.TRIAL, SubscriptionStatus.CANCELLED],
+        platforms, strict=False,
+    ):
+        sub = MerchantSubscription(
+            merchant_id=billing_merchant.id,
+            platform_id=platform.id,
+            tier_id=billing_tier.id,
+            status=status.value,
+            is_annual=False,
+            period_start=datetime.now(UTC),
+            period_end=datetime.now(UTC) + timedelta(days=30),
+        )
+        db.add(sub)
+        subs.append(sub)
+    db.commit()
+    for s in subs:
+        db.refresh(s)
+    return subs
+
+
+@pytest.mark.unit
+@pytest.mark.billing
+class TestBillingMetricsProviderMerchant:
+    """Tests for BillingMetricsProvider.get_merchant_metrics."""
+
+    def setup_method(self):
+        self.provider = BillingMetricsProvider()
+
+    def test_active_subscriptions_count(self, db, billing_merchant, billing_subscriptions):
+        """Counts active + trial subscriptions, excludes cancelled."""
+        metrics = self.provider.get_merchant_metrics(db, billing_merchant.id)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["billing.active_subscriptions"] == 2
+
+    def test_no_subscriptions(self, db, billing_merchant):
+        """Returns zero when merchant has no subscriptions."""
+        metrics = self.provider.get_merchant_metrics(db, billing_merchant.id)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["billing.active_subscriptions"] == 0
+
+    def test_nonexistent_merchant(self, db):
+        """Returns zero for a non-existent merchant ID."""
+        metrics = self.provider.get_merchant_metrics(db, 999999)
+        by_key = {m.key: m.value for m in metrics}
+        assert by_key["billing.active_subscriptions"] == 0