[
 {
  "name": "adding a driver half way: 120.00 more a year for 183 of 365 days is 60.16, plus a 25.00 fee",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 2500,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 183,
   "premiumChange": {
    "minor": 6016,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 2500,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 8516,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "one rounding of the difference, not two: pro-rating 500.00 and 620.00 separately would give 60.17",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 183,
   "premiumChange": {
    "minor": 6016,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 6016,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "removing the driver returns 60.16, less the 25.00 fee",
  "args": [
   {
    "minor": 62000,
    "currency": "GBP"
   },
   {
    "minor": 50000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 2500,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 183,
   "premiumChange": {
    "minor": -6016,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 2500,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": -3516,
    "currency": "GBP"
   },
   "kind": "return"
  }
 },
 {
  "name": "rounding up charges the part penny",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 183,
   "premiumChange": {
    "minor": 6017,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 6017,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "a change from inception is the whole difference",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-01-01",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 365,
   "premiumChange": {
    "minor": 12000,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 12000,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "a change on the expiry date costs nothing but the fee",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2027-01-01",
   {
    "minor": 2500,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 0,
   "premiumChange": {
    "minor": 0,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 2500,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 2500,
    "currency": "GBP"
   },
   "kind": "none"
  }
 },
 {
  "name": "a change with no premium effect still carries its fee",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 50000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-03-15",
   {
    "minor": 1500,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 292,
   "premiumChange": {
    "minor": 0,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 1500,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 1500,
    "currency": "GBP"
   },
   "kind": "none"
  }
 },
 {
  "name": "a leap-year term has 366 days: 366.00 more for the last 31 is 31.00",
  "args": [
   {
    "minor": 0,
    "currency": "GBP"
   },
   {
    "minor": 36600,
    "currency": "GBP"
   },
   "2028-01-01",
   "2029-01-01",
   "2028-12-01",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 366,
   "remainingDays": 31,
   "premiumChange": {
    "minor": 3100,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 3100,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "exactly half a penny rounds up half-up",
  "args": [
   {
    "minor": 10000,
    "currency": "GBP"
   },
   {
    "minor": 10001,
    "currency": "GBP"
   },
   "2026-01-01",
   "2026-01-05",
   "2026-01-03",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 4,
   "remainingDays": 2,
   "premiumChange": {
    "minor": 1,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 1,
    "currency": "GBP"
   },
   "kind": "additional"
  }
 },
 {
  "name": "exactly half a penny rounds to even: nothing to charge",
  "args": [
   {
    "minor": 10000,
    "currency": "GBP"
   },
   {
    "minor": 10001,
    "currency": "GBP"
   },
   "2026-01-01",
   "2026-01-05",
   "2026-01-03",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-even"
  ],
  "expect": {
   "totalDays": 4,
   "remainingDays": 2,
   "premiumChange": {
    "minor": 0,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 0,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 0,
    "currency": "GBP"
   },
   "kind": "none"
  }
 },
 {
  "name": "a return premium smaller than the fee still leaves something to pay",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 49000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 2500,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expect": {
   "totalDays": 365,
   "remainingDays": 183,
   "premiumChange": {
    "minor": -501,
    "currency": "GBP"
   },
   "adminFee": {
    "minor": 2500,
    "currency": "GBP"
   },
   "amountDue": {
    "minor": 1999,
    "currency": "GBP"
   },
   "kind": "return"
  }
 },
 {
  "name": "a change before inception is refused",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2025-12-31",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "changeDate must be from inceptionDate to expiryDate"
 },
 {
  "name": "a change after expiry is refused",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2027-01-02",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "changeDate must be from inceptionDate to expiryDate"
 },
 {
  "name": "expiry must be after inception",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2027-01-01",
   "2026-01-01",
   "2026-01-01",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "expiryDate must be after inceptionDate"
 },
 {
  "name": "a negative fee is refused",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": -1,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "adminFee must not be negative"
 },
 {
  "name": "a negative premium is refused",
  "args": [
   {
    "minor": -50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "GBP"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "premiums must not be negative"
 },
 {
  "name": "premiums in two currencies are refused",
  "args": [
   {
    "minor": 50000,
    "currency": "GBP"
   },
   {
    "minor": 62000,
    "currency": "EUR"
   },
   "2026-01-01",
   "2027-01-01",
   "2026-07-02",
   {
    "minor": 0,
    "currency": "GBP"
   },
   "half-up"
  ],
  "expectError": "currency mismatch"
 }
]