[zod-mock]: adds support for specifying ZodDiscriminatedUnion variant when discriminator value is set in stringMap options

[dforesman]

This change updates handling for ZodDiscriminatedUnion to generate a specific variant, if the value for the Discriminator key is defined in stringMap options.

This allows callers to generate mocks that adhere to a specific variant / member of the discriminated union.

Example

Let's say we have a discriminated union, split by the userType key:

const FirstType = z.object({
	userType: z.literal('type-1'),
	userName: z.string(),
});

const SecondType = z.object({
	userType: z.literal('type-2'),
	email: z.string(),
});

const Union = z.discriminatedUnion('userType', [FirstType, SecondType]);

Before

Previously, if you generated a mock from this union, and specified a known value for the userType field, there was no way to guarantee that the mocked object would be of the appropriate type :

const myMockObject = generateMock(Union, {
  stringMap: {
    userType: () => 'type-1'
  }
});
// myMockObject may randomly be either FirstType or SecondType

This is due to the specific variant being chosen randomly by faker's arrayElement helper.

After

With the changes in this PR, discriminator values in stringMap will be used to locate and generate the proper variant:

const myMockFirstTypeObject = generateMock(Union, {
  stringMap: {
    userType: () => 'type-1'
  }
});
// myMockFirstTypeObject is always FirstType

const myMockSecondTypeObject = generateMock(Union, {
  stringMap: {
    userType: () => 'type-2'
  }
});
// myMockSecondTypeObject is always SecondType

If the requested discriminator value is not found in the schema, generateMock will fall back to its existing behavior of randomly selecting a variant:

const myMockNonexistentTypeObject = generateMock(Union, {
  stringMap: {
    userType: () => 'type-3'
  }
});
// myMockNonexistentTypeObject falls back to randomly selecting a variant

const myMockUnspecifiedTypeObject = generateMock(Union);
// myMockUnspecifiedTypeObject randomly chooses a variant (existing behavior)

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 33be0bb

Command	Status	Duration	Result
nx affected:test --base=origin/main --codeCoverage	✅ Succeeded	21s	View ↗
nx affected:lint --base=origin/main	✅ Succeeded	3s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-07-30 23:19:19 UTC