Increase coverage for new module

Author: bkeepers

packages/neaps/src/index.ts

@@ -44,7 +44,7 @@ export function stationsNear(position: GeolibInputCoordinates, limit = 10) {
     .map((station) => ({ station, distance: getDistance(position, station) }))
     .sort((a, b) => a.distance - b.distance)
     .slice(0, limit)
-    .map(({ station, distance }) => createStation(station, distance))
+    .map(({ station, distance }) => useStation(station, distance))
 }
 
 /**
@@ -65,10 +65,10 @@ export function findStation(query: string) {
 
   if (!found) throw new Error(`Station not found: ${query}`)
 
-  return createStation(found)
+  return useStation(found)
 }
 
-function createStation(metadata: Station, distance?: number) {
+export function useStation(metadata: Station, distance?: number) {
   // Use MLLW as the default datum if available
   const defaultDatum = 'MLLW' in metadata.datums ? 'MLLW' : undefined
 
@@ -82,7 +82,7 @@ function createStation(metadata: Station, distance?: number) {
         const datumOffset = metadata.datums?.[datum]
         const mslOffset = metadata.datums?.['MSL']
 
-        if (!datum) {
+        if (!datumOffset) {
           throw new Error(
             `Station ${metadata.id} missing ${datum} datum. Available datums: ${Object.keys(metadata.datums || {}).join(', ')}`
           )

packages/neaps/test/index.test.ts

@@ -1,7 +1,9 @@
+import stations from '@neaps/tide-stations'
 import {
   getExtremesPrediction,
   nearestStation,
-  findStation
+  findStation,
+  useStation
 } from '../src/index.js'
 import { describe, test, expect } from 'vitest'
 
@@ -96,3 +98,63 @@ describe('findStation', () => {
     expect(station.getExtremesPrediction).toBeDefined()
   })
 })
+
+describe('datum', () => {
+  test('defaults to MLLW datum', () => {
+    const station = findStation('us-fl-ankona-indian-river')
+    const extremes = station.getExtremesPrediction({
+      start: new Date('2025-12-17T00:00:00Z'),
+      end: new Date('2025-12-18T00:00:00Z')
+    })
+    expect(extremes.datum).toBe('MLLW')
+  })
+
+  test('accepts datum option', () => {
+    const station = findStation('us-fl-ankona-indian-river')
+    const extremes = station.getExtremesPrediction({
+      start: new Date('2025-12-17T00:00:00Z'),
+      end: new Date('2025-12-18T00:00:00Z'),
+      datum: 'NAVD88'
+    })
+    expect(extremes.datum).toBe('NAVD88')
+  })
+
+  test('throws error for unavailable datum', () => {
+    const station = findStation('us-ma-boston')
+    expect(() => {
+      station.getExtremesPrediction({
+        start: new Date('2025-12-17T00:00:00Z'),
+        end: new Date('2025-12-18T00:00:00Z'),
+        datum: 'UNKNOWN_DATUM'
+      })
+    }).toThrow(/missing UNKNOWN_DATUM/)
+  })
+
+  test('throws error when missing MSL datum', () => {
+    // Find station without MSL but with other datums
+    const station = stations.find(
+      (s) => !('MSL' in s.datums) && Object.keys(s.datums).length > 0
+    )
+    if (!station) expect.fail('No station without MSL datum found')
+    expect(() => {
+      useStation(station).getExtremesPrediction({
+        start: new Date('2025-12-17T00:00:00Z'),
+        end: new Date('2025-12-18T00:00:00Z'),
+        datum: 'NAVD88'
+      })
+    }).toThrow(/missing MSL/)
+  })
+
+  test('does not apply datums when non available', () => {
+    // Find a station with no datums
+    const station = stations.find((s) => Object.entries(s.datums).length === 0)
+    if (!station) expect.fail('No station without datums found')
+    const extremes = useStation(station).getExtremesPrediction({
+      start: new Date('2025-12-17T00:00:00Z'),
+      end: new Date('2025-12-18T00:00:00Z')
+    })
+
+    expect(extremes.datum).toBeUndefined()
+    expect(extremes.predictions.length).toBeGreaterThan(0)
+  })
+})