diff --git a/plugins/woocommerce-blocks/assets/js/data/checkout/actions.ts b/plugins/woocommerce-blocks/assets/js/data/checkout/actions.ts
index 3e862e67bf3..e422c017cdf 100644
--- a/plugins/woocommerce-blocks/assets/js/data/checkout/actions.ts
+++ b/plugins/woocommerce-blocks/assets/js/data/checkout/actions.ts
@@ -92,22 +92,24 @@ export const setExtensionData = (
 	extensionData,
 } );
 
-export type CheckoutAction = ReturnOrGeneratorYieldUnion<
-	| typeof setPristine
-	| typeof setIdle
-	| typeof setComplete
-	| typeof setProcessing
-	| typeof setProcessingResponse
-	| typeof setBeforeProcessing
-	| typeof setAfterProcessing
-	| typeof setRedirectUrl
-	| typeof setHasError
-	| typeof incrementCalculating
-	| typeof decrementCalculating
-	| typeof setCustomerId
-	| typeof setOrderId
-	| typeof setUseShippingAsBilling
-	| typeof setShouldCreateAccount
-	| typeof setOrderNotes
-	| typeof setExtensionData
->;
+export type CheckoutAction =
+	| ReturnOrGeneratorYieldUnion<
+			| typeof setPristine
+			| typeof setIdle
+			| typeof setComplete
+			| typeof setProcessing
+			| typeof setProcessingResponse
+			| typeof setBeforeProcessing
+			| typeof setAfterProcessing
+			| typeof setRedirectUrl
+			| typeof setHasError
+			| typeof incrementCalculating
+			| typeof decrementCalculating
+			| typeof setCustomerId
+			| typeof setOrderId
+			| typeof setUseShippingAsBilling
+			| typeof setShouldCreateAccount
+			| typeof setOrderNotes
+			| typeof setExtensionData
+	  >
+	| Record< string, never >;
diff --git a/plugins/woocommerce-blocks/assets/js/data/checkout/reducers.ts b/plugins/woocommerce-blocks/assets/js/data/checkout/reducers.ts
index 7f2a4db12ca..c23651d92d8 100644
--- a/plugins/woocommerce-blocks/assets/js/data/checkout/reducers.ts
+++ b/plugins/woocommerce-blocks/assets/js/data/checkout/reducers.ts
@@ -1,7 +1,6 @@
 /**
  * External dependencies
  */
-import type { Reducer } from 'redux';
 import { PaymentResult } from '@woocommerce/types';
 
 /**
@@ -12,7 +11,7 @@ import { STATUS } from './constants';
 import { defaultState } from './default-state';
 import { CheckoutAction } from './actions';
 
-const reducer: Reducer = ( state = defaultState, action: CheckoutAction ) => {
+const reducer = ( state = defaultState, action: CheckoutAction ) => {
 	let newState = state;
 	switch ( action.type ) {
 		case types.SET_PRISTINE:
diff --git a/plugins/woocommerce-blocks/assets/js/data/checkout/test/reducer.ts b/plugins/woocommerce-blocks/assets/js/data/checkout/test/reducer.ts
new file mode 100644
index 00000000000..29597ff611c
--- /dev/null
+++ b/plugins/woocommerce-blocks/assets/js/data/checkout/test/reducer.ts
@@ -0,0 +1,274 @@
+/**
+ * Internal dependencies
+ */
+import reducer from '../reducers';
+import { defaultState } from '../default-state';
+import { STATUS } from '../constants';
+import * as actions from '../actions';
+
+describe.only( 'Checkout Store Reducer', () => {
+	it( 'should return the initial state', () => {
+		expect( reducer( undefined, {} ) ).toEqual( defaultState );
+	} );
+
+	it( 'should handle SET_PRISTINE', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.PRISTINE,
+		};
+
+		expect( reducer( defaultState, actions.setPristine() ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_IDLE', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+		};
+
+		expect( reducer( defaultState, actions.setIdle() ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_REDIRECT_URL', () => {
+		const expectedState = {
+			...defaultState,
+			redirectUrl: 'https://example.com',
+			status: STATUS.IDLE,
+		};
+
+		expect(
+			reducer(
+				defaultState,
+				actions.setRedirectUrl( 'https://example.com' )
+			)
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_PROCESSING_RESPONSE', () => {
+		const mockResponse = {
+			message: 'success',
+			redirectUrl: 'https://example.com',
+			paymentStatus: 'not set' as const,
+			paymentDetails: {},
+		};
+
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			processingResponse: mockResponse,
+		};
+
+		expect(
+			reducer(
+				defaultState,
+				actions.setProcessingResponse( mockResponse )
+			)
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_COMPLETE', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.COMPLETE,
+			redirectUrl: 'https://example.com',
+		};
+
+		expect(
+			reducer(
+				defaultState,
+				actions.setComplete( {
+					redirectUrl: 'https://example.com',
+				} )
+			)
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_PROCESSING', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.PROCESSING,
+		};
+
+		expect( reducer( defaultState, actions.setProcessing() ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_HAS_ERROR when status is PROCESSING', () => {
+		const initialState = { ...defaultState, status: STATUS.PROCESSING };
+
+		const expectedState = {
+			...defaultState,
+			hasError: true,
+			status: STATUS.IDLE,
+		};
+
+		expect( reducer( initialState, actions.setHasError( true ) ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_HAS_ERROR when status is BEFORE_PROCESSING', () => {
+		const initialState = {
+			...defaultState,
+			status: STATUS.BEFORE_PROCESSING,
+		};
+
+		const expectedState = {
+			...defaultState,
+			hasError: true,
+			status: STATUS.IDLE,
+		};
+
+		expect( reducer( initialState, actions.setHasError( true ) ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_HAS_ERROR when status is anything else', () => {
+		const initialState = { ...defaultState, status: STATUS.PRISTINE };
+
+		const expectedState = {
+			...defaultState,
+			hasError: false,
+			status: STATUS.IDLE,
+		};
+
+		expect( reducer( initialState, actions.setHasError( false ) ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_BEFORE_PROCESSING', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.BEFORE_PROCESSING,
+		};
+
+		expect(
+			reducer( defaultState, actions.setBeforeProcessing() )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_AFTER_PROCESSING', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.AFTER_PROCESSING,
+		};
+
+		expect( reducer( defaultState, actions.setAfterProcessing() ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle INCREMENT_CALCULATING', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			calculatingCount: 1,
+		};
+
+		expect(
+			reducer( defaultState, actions.incrementCalculating() )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle DECREMENT_CALCULATING', () => {
+		const initialState = {
+			...defaultState,
+			calculatingCount: 1,
+		};
+
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			calculatingCount: 0,
+		};
+
+		expect(
+			reducer( initialState, actions.decrementCalculating() )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_CUSTOMER_ID', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			customerId: 1,
+		};
+
+		expect( reducer( defaultState, actions.setCustomerId( 1 ) ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_ORDER_ID', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			orderId: 1,
+		};
+
+		expect( reducer( defaultState, actions.setOrderId( 1 ) ) ).toEqual(
+			expectedState
+		);
+	} );
+
+	it( 'should handle SET_SHIPPING_ADDRESS_AS_BILLING_ADDRESS', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			useShippingAsBilling: false,
+		};
+
+		expect(
+			reducer( defaultState, actions.setUseShippingAsBilling( false ) )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_SHOULD_CREATE_ACCOUNT', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			shouldCreateAccount: true,
+		};
+
+		expect(
+			reducer( defaultState, actions.setShouldCreateAccount( true ) )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_ORDER_NOTES', () => {
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			orderNotes: 'test',
+		};
+
+		expect(
+			reducer( defaultState, actions.setOrderNotes( 'test' ) )
+		).toEqual( expectedState );
+	} );
+
+	it( 'should handle SET_EXTENSION_DATA', () => {
+		const mockExtensionData = {
+			testExtension: { key: 'test', value: 'test2' },
+		};
+		const expectedState = {
+			...defaultState,
+			status: STATUS.IDLE,
+			extensionData: mockExtensionData,
+		};
+
+		expect(
+			reducer(
+				defaultState,
+				actions.setExtensionData( mockExtensionData )
+			)
+		).toEqual( expectedState );
+	} );
+} );