chore: create unit tests for defined

@xen-orchestra/defined/.USAGE.md

@@ -0,0 +1,21 @@
+The defined() function returns the first non-undefined value from a list of arguments, evaluating functions if needed.
+If only undefined values, return undefined.
+
+```js
+import defined from '@xen-orchestra/defined/index.js'
+
+defined(undefined, 'foo', 42)
+// Returns 'foo'
+
+defined([undefined, null, 10])
+// Returns [undefined, null, 10]
+
+defined([undefined, undefined], [undefined, undefined, 10])
+// Returns [undefined, undefined]
+
+defined(() => 'bar', 42)
+// Returns 'bar'
+
+defined(undefined, undefined)
+// Returns undefined
+```

@xen-orchestra/defined/README.md

@@ -14,6 +14,30 @@ Installation of the [npm package](https://npmjs.org/package/@xen-orchestra/defin
 npm install --save @xen-orchestra/defined
 ```
 
+## Usage
+
+The defined() function returns the first non-undefined value from a list of arguments, evaluating functions if needed.
+If only undefined values, return undefined.
+
+```js
+import defined from '@xen-orchestra/defined/index.js'
+
+defined(undefined, 'foo', 42)
+// Returns 'foo'
+
+defined([undefined, null, 10])
+// Returns [undefined, null, 10]
+
+defined([undefined, undefined], [undefined, undefined, 10])
+// Returns [undefined, undefined]
+
+defined(() => 'bar', 42)
+// Returns 'bar'
+
+defined(undefined, undefined)
+// Returns undefined
+```
+
 ## Contributions
 
 Contributions are _very_ welcomed, either on the documentation or on

@xen-orchestra/defined/defined.test.mjs

@@ -0,0 +1,29 @@
+import { describe, it } from 'node:test'
+import assert from 'node:assert/strict'
+import defined from '@xen-orchestra/defined/index.js'
+
+describe('Utilities to help handling (possibly) undefined values', () => {
+  it('should return first non undefined value in args', () => {
+    const expected = 'foo'
+    assert.deepStrictEqual(defined(undefined, 'foo', 42), expected)
+  })
+  it('should return first non undefined value in array', () => {
+    const expected = [undefined, null, 10]
+    assert.deepStrictEqual(defined([undefined, null, 10]), expected)
+  })
+  it('should return first non undefined value in arrays', () => {
+    const expected = [undefined, undefined, undefined]
+    assert.deepStrictEqual(defined([undefined, undefined, undefined], [undefined, undefined, 10]), expected)
+  })
+  it('should return first non undefined value in function', () => {
+    const expected = 'bar'
+    assert.deepStrictEqual(
+      defined(() => 'bar', 42),
+      expected
+    )
+  })
+  it('should return undefined if only undefined values', () => {
+    const expected = undefined
+    assert.equal(defined(undefined, undefined), expected)
+  })
+})