diff --git a/packages/lit-query/src/tests/infinite-and-options.test.ts b/packages/lit-query/src/tests/infinite-and-options.test.ts
index 6ef06b6cdc..701ea5e34c 100644
--- a/packages/lit-query/src/tests/infinite-and-options.test.ts
+++ b/packages/lit-query/src/tests/infinite-and-options.test.ts
@@ -364,7 +364,7 @@ describe('createInfiniteQueryController', () => {
 
     const nextPageResult = await infinite.fetchNextPage()
     expect(nextPageResult.isFetchNextPageError).toBe(true)
-    expect(nextPageResult.error).toBeInstanceOf(Error)
+    expect(nextPageResult.error).toEqual(new Error('next-page-failed'))
     await waitFor(() => infinite().isFetchNextPageError)
     expect(infinite().data?.pages).toEqual([0])
   })
diff --git a/packages/lit-query/src/tests/mutation-controller.test.ts b/packages/lit-query/src/tests/mutation-controller.test.ts
index e205ac0501..58ad85a5bf 100644
--- a/packages/lit-query/src/tests/mutation-controller.test.ts
+++ b/packages/lit-query/src/tests/mutation-controller.test.ts
@@ -164,7 +164,7 @@ describe('createMutationController', () => {
     await waitFor(() => mutation().isPending)
     await expect(errorPromise).rejects.toThrow('negative-not-allowed')
     await waitFor(() => mutation().isError)
-    expect(mutation().error).toBeInstanceOf(Error)
+    expect(mutation().error).toEqual(new Error('negative-not-allowed'))
   })
 
   it('M10: reset clears mutation state back to idle baseline', async () => {
@@ -188,7 +188,7 @@ describe('createMutationController', () => {
       'reset-target',
     )
     await waitFor(() => mutation().isError)
-    expect(mutation().error).toBeInstanceOf(Error)
+    expect(mutation().error).toEqual(new Error('reset-target'))
 
     mutation.reset()
     expect(mutation().isIdle).toBe(true)
@@ -221,7 +221,7 @@ describe('createMutationController', () => {
 
     expect(() => mutation.mutate(-1)).not.toThrow()
     await waitFor(() => mutation().isError)
-    expect(mutation().error).toBeInstanceOf(Error)
+    expect(mutation().error).toEqual(new Error('negative-not-allowed'))
 
     await expect(mutation.mutateAsync(-1)).rejects.toThrow(
       'negative-not-allowed',
diff --git a/packages/query-core/src/__tests__/timeoutManager.test.tsx b/packages/query-core/src/__tests__/timeoutManager.test.tsx
index 79ea130db8..d40101555e 100644
--- a/packages/query-core/src/__tests__/timeoutManager.test.tsx
+++ b/packages/query-core/src/__tests__/timeoutManager.test.tsx
@@ -93,7 +93,7 @@ describe('timeoutManager', () => {
           expect.stringMatching(
             /\[timeoutManager\]: Switching .* might result in unexpected behavior\..*/,
           ),
-          expect.anything(),
+          { previous: customProvider, provider: customProvider2 },
         )
 
         // 3. Switching again with no intermediate calls should not warn
diff --git a/packages/query-devtools/src/__tests__/Explorer.test.tsx b/packages/query-devtools/src/__tests__/Explorer.test.tsx
index 2ffc7cd1d9..5f2c1deab4 100644
--- a/packages/query-devtools/src/__tests__/Explorer.test.tsx
+++ b/packages/query-devtools/src/__tests__/Explorer.test.tsx
@@ -232,7 +232,7 @@ describe('Explorer', () => {
       ).toBeInTheDocument()
       expect(consoleError).toHaveBeenCalledWith(
         'Failed to copy: ',
-        expect.any(Error),
+        new Error('denied'),
       )
     })
 
diff --git a/packages/vue-query/src/__tests__/useQueryClient.test.ts b/packages/vue-query/src/__tests__/useQueryClient.test.ts
index 8811089184..a3d2c1a9d2 100644
--- a/packages/vue-query/src/__tests__/useQueryClient.test.ts
+++ b/packages/vue-query/src/__tests__/useQueryClient.test.ts
@@ -34,7 +34,9 @@ describe('useQueryClient', () => {
   it('should throw an error when queryClient does not exist in the context', () => {
     injectSpy.mockReturnValueOnce(undefined)
 
-    expect(useQueryClient).toThrow()
+    expect(useQueryClient).toThrow(
+      "No 'queryClient' found in Vue context, use 'VueQueryPlugin' to properly initialize the library.",
+    )
     expect(injectSpy).toHaveBeenCalledTimes(1)
     expect(injectSpy).toHaveBeenCalledWith(VUE_QUERY_CLIENT)
   })
@@ -42,7 +44,9 @@ describe('useQueryClient', () => {
   it('should throw an error when used outside of setup function', () => {
     hasInjectionContextSpy.mockReturnValueOnce(false)
 
-    expect(useQueryClient).toThrow()
+    expect(useQueryClient).toThrow(
+      'vue-query hooks can only be used inside setup() function or functions that support injection context.',
+    )
     expect(hasInjectionContextSpy).toHaveBeenCalledTimes(1)
   })