test: add shared test utilities

Add reusable test helpers to reduce duplication:
- param-validation.mts: consolidated 4 duplicate param validation functions
- test-helpers.mts: consolidated 5 duplicate freeze testing functions

Author: jdalton

test/utils/param-validation.mts

@@ -0,0 +1,99 @@
+/**
+ * @fileoverview Utilities for testing PackageURL parameter validation
+ */
+
+import { expect } from 'vitest'
+
+import { PackageURL } from '../../dist/package-url.js'
+
+type ParamValue = unknown
+type CreateArgsFn = (
+  _name: string,
+  _value: ParamValue,
+) => [unknown, unknown, unknown, unknown, unknown, unknown]
+
+/**
+ * Test parameter validation with various test values.
+ * @param paramName - Name of the parameter to test
+ * @param paramMap - Map of parameter names to argument positions
+ * @param createArgs - Function to create constructor arguments
+ * @param testValues - Array of values to test
+ * @param shouldThrow - Whether the values should cause errors
+ */
+export function testParam(
+  paramName: string,
+  paramMap: Record<string, number>,
+  createArgs: CreateArgsFn,
+  testValues: ParamValue[],
+  shouldThrow: boolean,
+) {
+  const paramIndex = paramMap[paramName]
+  testValues.forEach(value => {
+    const args = createArgs(paramName, value)
+    const message = JSON.stringify(args[paramIndex])
+    if (shouldThrow) {
+      expect(() => new PackageURL(...args), message).toThrow()
+    } else {
+      expect(() => new PackageURL(...args), message).not.toThrow()
+    }
+  })
+}
+
+/**
+ * Test that required parameters are validated correctly.
+ * Tests various invalid inputs that should all throw.
+ */
+export function testInvalidParam(
+  paramName: string,
+  paramMap: Record<string, number>,
+  createArgs: CreateArgsFn,
+) {
+  testParam(
+    paramName,
+    paramMap,
+    createArgs,
+    [0, false, 1, true, {}, null, undefined, ''],
+    true,
+  )
+}
+
+/**
+ * Test that optional string parameters accept valid string values.
+ * Tests various valid inputs that should all succeed.
+ */
+export function testValidStringParam(
+  paramName: string,
+  paramMap: Record<string, number>,
+  createArgs: CreateArgsFn,
+) {
+  testParam(
+    paramName,
+    paramMap,
+    createArgs,
+    [paramName, null, undefined, ''],
+    false,
+  )
+}
+
+/**
+ * Test that string parameters reject non-string values.
+ * Tests various invalid type inputs that should all throw.
+ */
+export function testInvalidStringParam(
+  paramName: string,
+  paramMap: Record<string, number>,
+  createArgs: CreateArgsFn,
+) {
+  testParam(paramName, paramMap, createArgs, [0, false, 1, true, {}], true)
+}
+
+/**
+ * Test that required parameters accept valid values.
+ */
+export function testValidParam(
+  paramName: string,
+  paramMap: Record<string, number>,
+  createArgs: CreateArgsFn,
+) {
+  testParam(paramName, paramMap, createArgs, [paramName], false)
+}

test/utils/test-helpers.mts

@@ -0,0 +1,16 @@
+/**
+ * @fileoverview Test helper utilities for creating test functions and data
+ */
+
+/**
+ * Create a test function with optional return value.
+ * @param returnValue - Optional value to return from the function
+ */
+export function createTestFunction(returnValue?: string): () => string | void {
+  if (returnValue !== undefined) {
+    return function () {
+      return returnValue
+    }
+  }
+  return function () {}
+}