diff --git a/__tests__/components/ui/select.test.tsx b/__tests__/components/ui/select.test.tsx
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+/**
+ * Tests for components/ui/select.tsx
+ *
+ * Covers three key states of the primitive:
+ *   1. Placeholder — shown when no value is selected
+ *   2. Value selection — selecting an item updates the displayed value
+ *   3. Disabled — interaction is blocked when the select is disabled
+ *
+ * Implementation notes
+ * ─────────────────────
+ * @base-ui/react Select renders its popup via a Portal into document.body.
+ * jsdom supports this, so we use userEvent.click to open the popup and
+ * select an item exactly as a user would.
+ *
+ * Placeholder state is signalled by `data-placeholder` on SelectTrigger
+ * (and SelectValue), per the base-ui Select API:
+ *   https://base-ui.com/react/components/select#trigger
+ *
+ * Disabled state is signalled by `data-disabled` on SelectTrigger and the
+ * native HTML `disabled` attribute on the underlying <button>.
+ */
+
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen, within } from '@testing-library/react'
+import userEvent from '@testing-library/user-event'
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from '@/components/ui/select'
+
+// ─── Shared test fixture ──────────────────────────────────────────────────────
+
+interface TestSelectProps {
+  value?: string
+  defaultValue?: string
+  onValueChange?: (value: string) => void
+  disabled?: boolean
+  placeholder?: string
+}
+
+/**
+ * Minimal but realistic Select assembly that mirrors how the component is
+ * used throughout the app. SelectContent is rendered without animation
+ * classes in jsdom so the items are immediately accessible after the popup
+ * opens.
+ */
+function TestSelect({
+  value,
+  defaultValue,
+  onValueChange,
+  disabled = false,
+  placeholder = 'Pick an option',
+}: TestSelectProps) {
+  return (
+    <Select
+      value={value}
+      defaultValue={defaultValue}
+      onValueChange={onValueChange}
+      disabled={disabled}
+    >
+      <SelectTrigger aria-label="test-select">
+        <SelectValue placeholder={placeholder} />
+      </SelectTrigger>
+      <SelectContent>
+        <SelectItem value="apple">Apple</SelectItem>
+        <SelectItem value="banana">Banana</SelectItem>
+        <SelectItem value="cherry">Cherry</SelectItem>
+      </SelectContent>
+    </Select>
+  )
+}
+
+// ─── Placeholder ──────────────────────────────────────────────────────────────
+
+describe('placeholder', () => {
+  it('shows the placeholder text when no value is selected', () => {
+    render(<TestSelect />)
+
+    // The SelectValue span renders the placeholder text as its content when
+    // no value is set.
+    expect(screen.getByText('Pick an option')).toBeInTheDocument()
+  })
+
+  it('marks the trigger with data-placeholder when no value is selected', () => {
+    render(<TestSelect />)
+
+    const trigger = screen.getByRole('button', { name: 'test-select' })
+
+    // base-ui sets data-placeholder on the trigger element when the select
+    // has no value — this is what drives the muted text-color in the CSS.
+    expect(trigger).toHaveAttribute('data-placeholder')
+  })
+
+  it('does not show data-placeholder once a value is set via defaultValue', () => {
+    render(<TestSelect defaultValue="apple" />)
+
+    const trigger = screen.getByRole('button', { name: 'test-select' })
+    expect(trigger).not.toHaveAttribute('data-placeholder')
+  })
+
+  it('does not render the placeholder text when a defaultValue is provided', () => {
+    render(<TestSelect defaultValue="banana" placeholder="Pick an option" />)
+
+    expect(screen.queryByText('Pick an option')).not.toBeInTheDocument()
+  })
+})
+
+// ─── Value selection ──────────────────────────────────────────────────────────
+
+describe('value selection', () => {
+  it('calls onValueChange with the selected item value when an option is clicked', async () => {
+    const user = userEvent.setup()
+    const onValueChange = vi.fn()
+
+    render(<TestSelect onValueChange={onValueChange} />)
+
+    // Open the popup
+    await user.click(screen.getByRole('button', { name: 'test-select' }))
+
+    // The popup is portalled into document.body — query from there
+    const listbox = await screen.findByRole('listbox')
+    await user.click(within(listbox).getByText('Cherry'))
+
+    expect(onValueChange).toHaveBeenCalledOnce()
+    expect(onValueChange).toHaveBeenCalledWith('cherry')
+  })
+
+  it('removes data-placeholder from the trigger after a selection is made', async () => {
+    const user = userEvent.setup()
+    let currentValue = ''
+    const onValueChange = vi.fn((v: string) => {
+      currentValue = v
+    })
+
+    const { rerender } = render(
+      <TestSelect value={currentValue} onValueChange={onValueChange} />,
+    )
+
+    const trigger = screen.getByRole('button', { name: 'test-select' })
+    expect(trigger).toHaveAttribute('data-placeholder')
+
+    // Open and select
+    await user.click(trigger)
+    const listbox = await screen.findByRole('listbox')
+    await user.click(within(listbox).getByText('Apple'))
+
+    expect(onValueChange).toHaveBeenCalledWith('apple')
+
+    // Rerender with the new value to reflect controlled state
+    rerender(<TestSelect value={currentValue} onValueChange={onValueChange} />)
+    expect(trigger).not.toHaveAttribute('data-placeholder')
+  })
+
+  it('displays the selected item label in the trigger after selection', async () => {
+    const user = userEvent.setup()
+    let currentValue = ''
+    const onValueChange = vi.fn((v: string) => {
+      currentValue = v
+    })
+
+    const { rerender } = render(
+      <TestSelect value={currentValue} onValueChange={onValueChange} />,
+    )
+
+    await user.click(screen.getByRole('button', { name: 'test-select' }))
+    const listbox = await screen.findByRole('listbox')
+    await user.click(within(listbox).getByText('Banana'))
+
+    rerender(<TestSelect value={currentValue} onValueChange={onValueChange} />)
+
+    // The trigger should now display the chosen item's label
+    expect(screen.getByRole('button', { name: 'test-select' })).toHaveTextContent('Banana')
+  })
+})
+
+// ─── Disabled state ───────────────────────────────────────────────────────────
+
+describe('disabled state', () => {
+  it('renders the trigger with the disabled attribute when the select is disabled', () => {
+    render(<TestSelect disabled />)
+
+    const trigger = screen.getByRole('button', { name: 'test-select' })
+    expect(trigger).toBeDisabled()
+  })
+
+  it('marks the trigger with data-disabled when disabled', () => {
+    render(<TestSelect disabled />)
+
+    const trigger = screen.getByRole('button', { name: 'test-select' })
+    expect(trigger).toHaveAttribute('data-disabled')
+  })
+
+  it('does not open the popup when the trigger is clicked while disabled', async () => {
+    const user = userEvent.setup()
+
+    render(<TestSelect disabled />)
+
+    await user.click(screen.getByRole('button', { name: 'test-select' }))
+
+    // No listbox should appear in the document after clicking a disabled trigger
+    expect(screen.queryByRole('listbox')).not.toBeInTheDocument()
+  })
+
+  it('does not call onValueChange when disabled', async () => {
+    const user = userEvent.setup()
+    const onValueChange = vi.fn()
+
+    render(<TestSelect disabled onValueChange={onValueChange} />)
+
+    await user.click(screen.getByRole('button', { name: 'test-select' }))
+
+    expect(onValueChange).not.toHaveBeenCalled()
+  })
+})