diff --git a/packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.jsx.snap b/packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.tsx.snap
similarity index 99%
rename from packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.jsx.snap
rename to packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.tsx.snap
index 16ddce595..80064f5d3 100644
--- a/packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.jsx.snap
+++ b/packages/inferno-test-utils/__tests__/__snapshots__/snapshots.spec.tsx.snap
@@ -151,7 +151,7 @@ exports[`Snapshots JSX Should render fragment root 1`] = `
 
 exports[`Snapshots JSX Should render html element 1`] = `
 <a
-  aria-colspan="3"
+  aria-colspan={3}
   className="foo"
   onClick={[Function]}
 >
diff --git a/packages/inferno-test-utils/__tests__/__snapshots__/testUtils.jest.spec.jsx.snap b/packages/inferno-test-utils/__tests__/__snapshots__/testUtils.jest.spec.tsx.snap
similarity index 100%
rename from packages/inferno-test-utils/__tests__/__snapshots__/testUtils.jest.spec.jsx.snap
rename to packages/inferno-test-utils/__tests__/__snapshots__/testUtils.jest.spec.tsx.snap
diff --git a/packages/inferno-test-utils/__tests__/snapshots.spec.jsx b/packages/inferno-test-utils/__tests__/snapshots.spec.tsx
similarity index 89%
rename from packages/inferno-test-utils/__tests__/snapshots.spec.jsx
rename to packages/inferno-test-utils/__tests__/snapshots.spec.tsx
index e8bac4957..5ab6e709f 100644
--- a/packages/inferno-test-utils/__tests__/snapshots.spec.jsx
+++ b/packages/inferno-test-utils/__tests__/snapshots.spec.tsx
@@ -2,7 +2,7 @@ import { Component, createFragment, Fragment } from 'inferno';
 import { renderToSnapshot } from 'inferno-test-utils';
 import { ChildFlags } from 'inferno-vnode-flags';
 
-if (window.usingJest) {
+if ((window as any).usingJest) {
   describe('Snapshots', () => {
     class Foobar extends Component {
       render({ children }) {
@@ -37,7 +37,7 @@ if (window.usingJest) {
       it('Should render html element', () => {
         expect(
           renderToSnapshot(
-            <a onClick={() => {}} aria-colspan="3" className="foo">
+            <a onClick={() => {}} aria-colspan={3} className="foo">
               Bar
             </a>,
           ),
@@ -142,13 +142,19 @@ if (window.usingJest) {
       });
 
       it('Should not fail when returning children array from component root, which contains text node. Github #1404', () => {
+        interface LabelProps {
+          label?: string;
+          htmlFor?: string;
+          optional?: boolean;
+          children: any;
+        }
         const Label = ({
           label,
           htmlFor,
           children,
           optional = false,
           ...props
-        }) => {
+        }: LabelProps) => {
           if (optional && !label) {
             return children;
           }
@@ -180,13 +186,19 @@ if (window.usingJest) {
       });
 
       it('Should not fail when returning children array from component root, Github #1404', () => {
+        interface LabelProps {
+          label?: string;
+          htmlFor?: string;
+          optional?: boolean;
+          children: any;
+        }
         const Label = ({
-          label,
-          htmlFor,
-          children,
-          optional = false,
-          ...props
-        }) => {
+                         label,
+                         htmlFor,
+                         children,
+                         optional = false,
+                         ...props
+                       }: LabelProps) => {
           if (optional && !label) {
             return children;
           }
@@ -208,12 +220,8 @@ if (window.usingJest) {
 
       it('Should flush setStates before building snapshot', () => {
         class App extends Component {
-          constructor(props) {
-            super(props);
-
-            this.state = {
-              foo: '',
-            };
+          state = {
+            foo: ''
           }
 
           componentDidMount() {
diff --git a/packages/inferno-test-utils/__tests__/testUtils.jest.spec.jsx b/packages/inferno-test-utils/__tests__/testUtils.jest.spec.tsx
similarity index 96%
rename from packages/inferno-test-utils/__tests__/testUtils.jest.spec.jsx
rename to packages/inferno-test-utils/__tests__/testUtils.jest.spec.tsx
index f16e994f9..b27f17da0 100644
--- a/packages/inferno-test-utils/__tests__/testUtils.jest.spec.jsx
+++ b/packages/inferno-test-utils/__tests__/testUtils.jest.spec.tsx
@@ -5,7 +5,7 @@ const FunctionalComponent = function (props) {
   return createElement('div', props);
 };
 
-const usingJest = window.usingJest;
+const usingJest = (window as any).usingJest as boolean;
 
 describe('renderToSnapshot', () => {
   it('should return a snapshot from a valid vNode', () => {
diff --git a/packages/inferno-test-utils/__tests__/testUtils.spec.jsx b/packages/inferno-test-utils/__tests__/testUtils.spec.tsx
similarity index 94%
rename from packages/inferno-test-utils/__tests__/testUtils.spec.jsx
rename to packages/inferno-test-utils/__tests__/testUtils.spec.tsx
index 7dd4de691..26d657ca2 100644
--- a/packages/inferno-test-utils/__tests__/testUtils.spec.jsx
+++ b/packages/inferno-test-utils/__tests__/testUtils.spec.tsx
@@ -180,11 +180,11 @@ describe('Test Utils', () => {
 
     it('should return false for VNodes of incorrect type', () => {
       expect(isDOMVNodeOfType(createElement('div'), 'foo')).toBe(false);
-      expect(isDOMVNodeOfType(createElement('div'), {})).toBe(false);
-      expect(isDOMVNodeOfType(createElement('div'), [])).toBe(false);
-      expect(isDOMVNodeOfType(createElement('div'), 10)).toBe(false);
-      expect(isDOMVNodeOfType(createElement('div'), undefined)).toBe(false);
-      expect(isDOMVNodeOfType(createElement('div'), null)).toBe(false);
+      expect(isDOMVNodeOfType(createElement('div'), {} as never)).toBe(false);
+      expect(isDOMVNodeOfType(createElement('div'), [] as never)).toBe(false);
+      expect(isDOMVNodeOfType(createElement('div'), 10 as never)).toBe(false);
+      expect(isDOMVNodeOfType(createElement('div'), undefined as never)).toBe(false);
+      expect(isDOMVNodeOfType(createElement('div'), null as never)).toBe(false);
     });
   });
 
@@ -333,13 +333,13 @@ describe('Test Utils', () => {
 
     it('should return false for DOMElements of incorrect type', () => {
       expect(isDOMElementOfType(createDOMElement('div'), 'foo')).toBe(false);
-      expect(isDOMElementOfType(createDOMElement('div'), {})).toBe(false);
-      expect(isDOMElementOfType(createDOMElement('div'), [])).toBe(false);
-      expect(isDOMElementOfType(createDOMElement('div'), 10)).toBe(false);
-      expect(isDOMElementOfType(createDOMElement('div'), undefined)).toBe(
+      expect(isDOMElementOfType(createDOMElement('div'), {} as never)).toBe(false);
+      expect(isDOMElementOfType(createDOMElement('div'), [] as never)).toBe(false);
+      expect(isDOMElementOfType(createDOMElement('div'), 10 as never)).toBe(false);
+      expect(isDOMElementOfType(createDOMElement('div'), undefined as never)).toBe(
         false,
       );
-      expect(isDOMElementOfType(createDOMElement('div'), null)).toBe(false);
+      expect(isDOMElementOfType(createDOMElement('div'), null as never)).toBe(false);
     });
   });
 
@@ -411,7 +411,7 @@ describe('Test Utils', () => {
       expect(
         isRenderedClassComponentOfType(
           renderIntoContainer(createClassVNode),
-          'div',
+          'div' as never,
         ),
       ).toBe(false);
 
@@ -436,7 +436,7 @@ describe('Test Utils', () => {
       expect(
         isRenderedClassComponentOfType(
           renderIntoContainer(extendClassVNode),
-          'div',
+          'div' as never,
         ),
       ).toBe(false);
     });
@@ -459,6 +459,8 @@ describe('Test Utils', () => {
       expect(spy).not.toHaveBeenCalled();
       findAllInRenderedTree(tree1, (args) => {
         spy(args.type);
+
+        return true
       });
       // 0: section
       // 1: FunctionalComponent
@@ -470,8 +472,11 @@ describe('Test Utils', () => {
     });
 
     it('should call predicate in the correct order', () => {
-      const types = [];
-      findAllInRenderedTree(tree1, ({ type }) => types.push(type));
+      const types: unknown[] = [];
+      findAllInRenderedTree(tree1, ({ type }) => {
+        types.push(type)
+        return true
+      });
       expect(types).toEqual(['section', FunctionalComponent, 'div']);
     });
 
@@ -507,8 +512,7 @@ describe('Test Utils', () => {
     );
 
     it('should throw an error when not passed a VNode', () => {
-      const errorRegex = /findAllInVNodeTree/;
-      const predicate = (vNode) => {
+      const predicate = () => {
         return true;
       };
       const testValue = (value) => {
@@ -534,6 +538,7 @@ describe('Test Utils', () => {
 
       findAllInVNodeTree(tree2, (args) => {
         predicate(args.type);
+        return true;
       });
       // 0: section
       // 1: FunctionalComponent
@@ -543,8 +548,11 @@ describe('Test Utils', () => {
     });
 
     it('should call predicate in the correct order', () => {
-      const types = [];
-      findAllInVNodeTree(tree2, ({ type }) => types.push(type));
+      const types: unknown[] = [];
+      findAllInVNodeTree(tree2, ({ type }) => {
+        types.push(type);
+        return true;
+      });
       expect(types).toEqual(['section', FunctionalComponent]);
     });
   });
@@ -616,7 +624,7 @@ describe('Test Utils', () => {
     );
 
     it('should return an array of matched DOM elements', () => {
-      const testValue = (tagName, length, instance) => {
+      const testValue = (tagName, length) => {
         const result = scryRenderedDOMElementsWithTag(tree4, tagName);
         expect(result instanceof Array).toBeTruthy();
         expect(result.length).toBe(length);
@@ -708,7 +716,6 @@ describe('Test Utils', () => {
     );
 
     it('should throw an error when more than one result is found #1', () => {
-      const errorRegex = /Did not find exactly one match/;
       const testValue = (classNames) => {
         expect(() => {
           findRenderedDOMElementWithClass(tree7, classNames);
@@ -719,7 +726,7 @@ describe('Test Utils', () => {
     });
 
     it('should return a matched DOM element', () => {
-      const testValue = (classNames, instance) => {
+      const testValue = (classNames) => {
         const result = findRenderedDOMElementWithClass(tree7, classNames);
         const arrOfClassName = classNames.split(' ');
         for (let i = 0; i < arrOfClassName.length; i++) {
@@ -762,7 +769,6 @@ describe('Test Utils', () => {
     );
 
     it('should throw an error when more than one result is found #2', () => {
-      const errorRegex = /Did not find exactly one match/;
       const testValue = (tagName) => {
         expect(() => {
           findRenderedDOMElementWithTag(tree8, tagName);
@@ -773,7 +779,7 @@ describe('Test Utils', () => {
     });
 
     it('should return a matched DOM element', () => {
-      const testValue = (tagName, instance) => {
+      const testValue = (tagName) => {
         const result = findRenderedDOMElementWithTag(tree8, tagName);
 
         expect(result.tagName).toBe(tagName.toUpperCase());
@@ -796,7 +802,6 @@ describe('Test Utils', () => {
     );
 
     it('should throw an error when more than one result is found #3', () => {
-      const errorRegex = /Did not find exactly one match/;
       const testValue = (type) => {
         expect(() => {
           findRenderedVNodeWithType(tree9, type);
@@ -834,7 +839,6 @@ describe('Test Utils', () => {
     );
 
     it('should throw an error when more than one result is found #4', () => {
-      const errorRegex = /Did not find exactly one match/;
       const testValue = (type) => {
         expect(() => {
           findVNodeWithType(tree10, type);