add test + fix two bugs

Author: severo

src/helpers/dataframeV2.ts

@@ -60,17 +60,8 @@ export function arrayDataFrame(data: Cells[]): DataFrameV2 {
       },
     }
   }
-  if (!(0 in data)) {
-    return {
-      numRows: 0,
-      header: [],
-      getCell: () => undefined,
-      fetch,
-      eventTarget,
-    }
-  }
 
-  const header = Object.keys(data[0])
+  const header = 0 in data ? Object.keys(data[0]) : []
 
   return {
     numRows: data.length,
@@ -90,7 +81,7 @@ export function arrayDataFrame(data: Cells[]): DataFrameV2 {
         throw new Error(`Column "${column}" not found in row ${row}`)
       }
       // Return a resolved value (which might be undefined as well)
-      return { value: data[row] }
+      return { value: cells[column] }
       // Note that this function never returns undefined (meaning pending cell), because the data is static.
     },
     fetch,

test/helpers/dataframeV2.test.ts

@@ -0,0 +1,51 @@
+import { describe, expect, it } from 'vitest'
+import { arrayDataFrame } from '../../src/helpers/dataframeV2.js'
+
+describe('arrayDataFrame', () => {
+  const testData = [
+    { id: 1, name: 'Alice', age: 30 },
+    { id: 2, name: 'Bob', age: 25 },
+    { id: 3, name: 'Charlie', age: 35 },
+  ]
+
+  it('should create a DataFrame with correct header and numRows', () => {
+    const df = arrayDataFrame(testData)
+    expect(df.header).toEqual(['id', 'name', 'age'])
+    expect(df.numRows).toBe(3)
+  })
+
+  it('should return the cell value without first fetching the column', () => {
+    const df = arrayDataFrame(testData)
+    const cell = df.getCell({ row: 1, column: 'name' })
+    expect(cell?.value).toBe('Bob')
+  })
+
+  it('should throw if accessing data from an unknown column', () => {
+    const df = arrayDataFrame(testData)
+    expect(() => {
+      df.getCell({ row: 0, column: 'doesnotexist' } )
+    }).toThrow('Invalid column: doesnotexist')
+  })
+
+  it('should throw if accessing data from an unknown row', () => {
+    const df = arrayDataFrame(testData)
+    expect(() => {
+      df.getCell({ row: 3, column: 'id' } )
+    }).toThrow('Invalid row index: 3')
+  })
+
+  it('should throw if accessing data from an empty array', () => {
+    const df = arrayDataFrame([])
+    expect(df.header).toEqual([])
+    expect(df.numRows).toBe(0)
+    expect(() => {
+      df.getCell({ row: 0, column: 'name' } )
+    }).toThrow('Invalid row index: 0')
+  })
+
+  it('provides fetch, even if it\'s a no-op function', () => {
+    const df = arrayDataFrame([])
+    expect(df.fetch).toBeDefined()
+  })
+
+})