From a8a42908bf70c2472a3bf37f076a87a318a44ffe Mon Sep 17 00:00:00 2001
From: Wonsuk Choi <sukvvon@gmail.com>
Date: Thu, 1 Oct 2026 01:12:32 +0900
Subject: [PATCH] test(lit-query/createMutationController): add type tests

---
 .../createMutationController.test-d.ts        | 249 ++++++++++++++++++
 1 file changed, 249 insertions(+)
 create mode 100644 packages/lit-query/src/__tests__/createMutationController.test-d.ts

diff --git a/packages/lit-query/src/__tests__/createMutationController.test-d.ts b/packages/lit-query/src/__tests__/createMutationController.test-d.ts
new file mode 100644
index 0000000000..ecce6f8d69
--- /dev/null
+++ b/packages/lit-query/src/__tests__/createMutationController.test-d.ts
@@ -0,0 +1,249 @@
+import { QueryClient } from '@tanstack/query-core'
+import { LitElement } from 'lit'
+import { describe, expectTypeOf, it } from 'vitest'
+import { createMutationController } from '../createMutationController.js'
+import type {
+  DefaultError,
+  MutationFunctionContext,
+  MutationKey,
+} from '@tanstack/query-core'
+import type { MutationResultAccessor } from '../createMutationController.js'
+
+class Host extends LitElement {}
+
+describe('createMutationController', () => {
+  it('should infer TData from mutationFn return type', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation().data).toEqualTypeOf<string | undefined>()
+    expectTypeOf(mutation().error).toEqualTypeOf<DefaultError | null>()
+  })
+
+  it('should infer TVariables from mutationFn parameter', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: (vars: { id: string }) => Promise.resolve(vars.id),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation.mutate).toBeCallableWith({ id: '1' })
+    expectTypeOf(mutation().data).toEqualTypeOf<string | undefined>()
+  })
+
+  it('should infer TOnMutateResult from onMutate return type', () => {
+    createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+        onMutate: () => {
+          return { token: 'abc' }
+        },
+        onSuccess: (_data, _variables, onMutateResult) => {
+          expectTypeOf(onMutateResult).toEqualTypeOf<{ token: string }>()
+        },
+        onError: (_error, _variables, onMutateResult) => {
+          expectTypeOf(onMutateResult).toEqualTypeOf<
+            { token: string } | undefined
+          >()
+        },
+      },
+      new QueryClient(),
+    )
+  })
+
+  it('should allow explicit generic types', () => {
+    const mutation = createMutationController<string, Error, { id: number }>(
+      new Host(),
+      {
+        mutationFn: (vars) => {
+          expectTypeOf(vars).toEqualTypeOf<{ id: number }>()
+          return Promise.resolve('result')
+        },
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation().data).toEqualTypeOf<string | undefined>()
+    expectTypeOf(mutation().error).toEqualTypeOf<Error | null>()
+  })
+
+  it('should return correct MutationResultAccessor type', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve(42),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation).toEqualTypeOf<
+      MutationResultAccessor<number, DefaultError, void, unknown>
+    >()
+  })
+
+  it('should type mutateAsync with correct return type', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: (id: string) => Promise.resolve(id.length),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation.mutateAsync).toBeCallableWith('test')
+    expectTypeOf(mutation.mutateAsync('test')).toEqualTypeOf<Promise<number>>()
+  })
+
+  it('should default TVariables to void when mutationFn has no parameters', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation.mutate).toBeCallableWith()
+  })
+
+  it('should allow calling mutate with no arguments when TVariables is optional undefinable', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: (_variables: number | undefined) => Promise.resolve(1),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation.mutate).toBeCallableWith()
+    expectTypeOf(mutation.mutateAsync).toBeCallableWith()
+  })
+
+  it('should infer custom TError type', () => {
+    class CustomError extends Error {
+      code: number
+      constructor(code: number) {
+        super()
+        this.code = code
+      }
+    }
+
+    const mutation = createMutationController<string, CustomError>(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+      },
+      new QueryClient(),
+    )
+
+    expectTypeOf(mutation().error).toEqualTypeOf<CustomError | null>()
+    expectTypeOf(mutation().data).toEqualTypeOf<string | undefined>()
+  })
+
+  it('should infer types for onSettled callback', () => {
+    createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve(42),
+        onSettled: (data, error, _variables, _onMutateResult) => {
+          expectTypeOf(data).toEqualTypeOf<number | undefined>()
+          expectTypeOf(error).toEqualTypeOf<DefaultError | null>()
+        },
+      },
+      new QueryClient(),
+    )
+  })
+
+  it('should infer custom TError in onError callback', () => {
+    class CustomError extends Error {
+      code: number
+      constructor(code: number) {
+        super()
+        this.code = code
+      }
+    }
+
+    createMutationController<string, CustomError>(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+        onError: (error) => {
+          expectTypeOf(error).toEqualTypeOf<CustomError>()
+        },
+      },
+      new QueryClient(),
+    )
+  })
+
+  it('should type context as the last argument for mutationFn and every hook-level callback', () => {
+    createMutationController(
+      new Host(),
+      {
+        mutationFn: (_variables, context) => {
+          expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+          expectTypeOf(context.client).toEqualTypeOf<QueryClient>()
+          return Promise.resolve('data')
+        },
+        onMutate: (_variables, context) => {
+          expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+        },
+        onSuccess: (_data, _variables, _onMutateResult, context) => {
+          expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+        },
+        onError: (_error, _variables, _onMutateResult, context) => {
+          expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+        },
+        onSettled: (_data, _error, _variables, _onMutateResult, context) => {
+          expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+        },
+      },
+      new QueryClient(),
+    )
+  })
+
+  it('should type context as the last argument for every per-call mutate option', () => {
+    const mutation = createMutationController(
+      new Host(),
+      {
+        mutationFn: () => Promise.resolve('data'),
+      },
+      new QueryClient(),
+    )
+
+    mutation.mutate(undefined, {
+      onSuccess: (_data, _variables, _onMutateResult, context) => {
+        expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+      },
+      onError: (_error, _variables, _onMutateResult, context) => {
+        expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+      },
+      onSettled: (_data, _error, _variables, _onMutateResult, context) => {
+        expectTypeOf(context).toEqualTypeOf<MutationFunctionContext>()
+      },
+    })
+  })
+
+  it('should type context.mutationKey as MutationKey', () => {
+    createMutationController(
+      new Host(),
+      {
+        mutationKey: ['todos', 'add'] as const,
+        mutationFn: () => Promise.resolve('data'),
+        onSuccess: (_data, _variables, _onMutateResult, context) => {
+          expectTypeOf(context.mutationKey).toEqualTypeOf<
+            MutationKey | undefined
+          >()
+        },
+      },
+      new QueryClient(),
+    )
+  })
+})