diff --git a/packages/core/lib/__tests__/reducer.spec.tsx b/packages/core/lib/__tests__/reducer.spec.tsx
new file mode 100644
index 000000000..d66fcbd6c
--- /dev/null
+++ b/packages/core/lib/__tests__/reducer.spec.tsx
@@ -0,0 +1,478 @@
+import {
+  DuplicateAction,
+  InsertAction,
+  MoveAction,
+  RegisterZoneAction,
+  RemoveAction,
+  ReorderAction,
+  ReplaceAction,
+  SetDataAction,
+  UnregisterZoneAction,
+  createReducer,
+} from "../reducer";
+import { Config, Data } from "../../types/Config";
+import { rootDroppableId } from "../root-droppable-id";
+
+import { generateId } from "../generate-id";
+
+jest.mock("../generate-id");
+
+const mockedGenerateId = generateId as jest.MockedFunction<typeof generateId>;
+
+type Props = {
+  Comp: {
+    prop: string;
+  };
+};
+const defaultData: Data = { root: { title: "" }, content: [], zones: {} };
+
+describe("Reducer", () => {
+  const config: Config<Props> = {
+    components: {
+      Comp: {
+        defaultProps: { prop: "example" },
+        render: () => <div />,
+      },
+    },
+  };
+
+  const reducer = createReducer({ config });
+
+  describe("insert action", () => {
+    it("should insert into rootDroppableId", () => {
+      const state: Data = { ...defaultData };
+
+      const action: InsertAction = {
+        type: "insert",
+        componentType: "Comp",
+        destinationIndex: 0,
+        destinationZone: rootDroppableId,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content[0]).toHaveProperty("type", "Comp");
+      expect(newState.content[0].props).toHaveProperty("prop", "example");
+    });
+
+    it("should insert into a different zone", () => {
+      const state: Data = { ...defaultData };
+      const action: InsertAction = {
+        type: "insert",
+        componentType: "Comp",
+        destinationIndex: 0,
+        destinationZone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1[0]).toHaveProperty("type", "Comp");
+
+      expect(newState.zones?.zone1[0].props).toHaveProperty("prop", "example");
+    });
+  });
+
+  describe("reorder action", () => {
+    it("should reorder within rootDroppableId", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [
+          { type: "Comp", props: { id: "1" } },
+          { type: "Comp", props: { id: "2" } },
+        ],
+      };
+      const action: ReorderAction = {
+        type: "reorder",
+        sourceIndex: 0,
+        destinationIndex: 1,
+        destinationZone: rootDroppableId,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content[0].props.id).toBe("2");
+      expect(newState.content[1].props.id).toBe("1");
+    });
+
+    it("should reorder within a different zone", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: {
+          zone1: [
+            { type: "A", props: { id: "1" } },
+            { type: "B", props: { id: "2" } },
+          ],
+        },
+      };
+      const action: ReorderAction = {
+        type: "reorder",
+        sourceIndex: 0,
+        destinationIndex: 1,
+        destinationZone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1[0].props.id).toBe("2");
+      expect(newState.zones?.zone1[1].props.id).toBe("1");
+    });
+  });
+
+  describe("duplicate action", () => {
+    it("should duplicate in content", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [
+          {
+            type: "Comp",
+            props: { id: "sampleId", prop: "Some example data" },
+          },
+        ],
+      };
+      const action: DuplicateAction = {
+        type: "duplicate",
+        sourceIndex: 0,
+        sourceZone: rootDroppableId,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content).toHaveLength(2);
+      expect(newState.content[1].props.id).not.toBe("sampleId");
+      expect(newState.content[1].props.prop).toBe("Some example data");
+    });
+
+    it("should duplicate in a different zone", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: {
+          zone1: [
+            {
+              type: "Comp",
+              props: { id: "sampleId", prop: "Some example data" },
+            },
+          ],
+        },
+      };
+      const action: DuplicateAction = {
+        type: "duplicate",
+        sourceIndex: 0,
+        sourceZone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1).toHaveLength(2);
+      expect(newState.zones?.zone1[1].props.id).not.toBe("sampleId");
+      expect(newState.zones?.zone1[1].props.prop).toBe("Some example data");
+    });
+
+    it("should recursively duplicate items", () => {
+      let counter = 0;
+
+      mockedGenerateId.mockImplementation(() => `mockId-${counter++}`);
+
+      const state: Data = {
+        ...defaultData,
+        zones: {
+          zone1: [
+            {
+              type: "Comp",
+              props: { id: "mycomponent", prop: "Some example data" },
+            },
+          ],
+          "mycomponent:zone1": [
+            {
+              type: "Comp",
+              props: { id: "sampleId", prop: "More example data" },
+            },
+          ],
+        },
+      };
+
+      const action: DuplicateAction = {
+        type: "duplicate",
+        sourceIndex: 0,
+        sourceZone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+
+      expect(newState).toMatchInlineSnapshot(`
+        {
+          "content": [],
+          "root": {
+            "title": "",
+          },
+          "zones": {
+            "mockId-0:zone1": [
+              {
+                "props": {
+                  "id": "mockId-1",
+                  "prop": "More example data",
+                },
+                "type": "Comp",
+              },
+            ],
+            "mycomponent:zone1": [
+              {
+                "props": {
+                  "id": "sampleId",
+                  "prop": "More example data",
+                },
+                "type": "Comp",
+              },
+            ],
+            "zone1": [
+              {
+                "props": {
+                  "id": "mycomponent",
+                  "prop": "Some example data",
+                },
+                "type": "Comp",
+              },
+              {
+                "props": {
+                  "id": "mockId-0",
+                  "prop": "Some example data",
+                },
+                "type": "Comp",
+              },
+            ],
+          },
+        }
+      `);
+    });
+  });
+
+  describe("move action", () => {
+    it("should move from rootDroppableId to another zone", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [{ type: "Comp", props: { id: "1" } }],
+        zones: { zone1: [{ type: "Comp", props: { id: "2" } }] },
+      };
+      const action: MoveAction = {
+        type: "move",
+        sourceIndex: 0,
+        sourceZone: rootDroppableId,
+        destinationIndex: 1,
+        destinationZone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content).toHaveLength(0);
+      expect(newState.zones?.zone1[1].props.id).toBe("1");
+    });
+
+    it("should move from a zone to rootDroppableId", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [{ type: "Comp", props: { id: "1" } }],
+        zones: { zone1: [{ type: "Comp", props: { id: "2" } }] },
+      };
+      const action: MoveAction = {
+        type: "move",
+        sourceIndex: 0,
+        sourceZone: "zone1",
+        destinationIndex: 1,
+        destinationZone: rootDroppableId,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1).toHaveLength(0);
+      expect(newState.content[1].props.id).toBe("2");
+    });
+
+    it("should move between two zones", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [],
+        zones: {
+          zone1: [{ type: "Comp", props: { id: "1" } }],
+          zone2: [{ type: "Comp", props: { id: "2" } }],
+        },
+      };
+      const action: MoveAction = {
+        type: "move",
+        sourceIndex: 0,
+        sourceZone: "zone1",
+        destinationIndex: 0, // Go to the start, this time
+        destinationZone: "zone2",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1).toHaveLength(0);
+      expect(newState.zones?.zone2[0].props.id).toBe("1");
+    });
+  });
+
+  describe("replace action", () => {
+    const replacement = { type: "Comp", props: { id: "3" } };
+
+    it("should replace in content", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [{ type: "Comp", props: { id: "1" } }],
+      };
+      const action: ReplaceAction = {
+        type: "replace",
+        destinationIndex: 0,
+        destinationZone: rootDroppableId,
+        data: replacement,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content.length).toBe(1);
+      expect(newState.content[0].props.id).toBe("3");
+    });
+
+    it("should replace in a zone", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: { zone1: [{ type: "Comp", props: { id: "1" } }] },
+      };
+      const action: ReplaceAction = {
+        type: "replace",
+        destinationIndex: 0,
+        destinationZone: "zone1",
+        data: replacement,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1.length).toBe(1);
+      expect(newState.zones?.zone1[0].props.id).toBe("3");
+    });
+  });
+
+  describe("remove action", () => {
+    it("should remove from content", () => {
+      const state: Data = {
+        ...defaultData,
+        content: [{ type: "Comp", props: { id: "1" } }],
+      };
+      const action: RemoveAction = {
+        type: "remove",
+        index: 0,
+        zone: rootDroppableId,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.content).toHaveLength(0);
+    });
+
+    it("should remove from a zone", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: { zone1: [{ type: "Comp", props: { id: "1" } }] },
+      };
+      const action: RemoveAction = {
+        type: "remove",
+        index: 0,
+        zone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1).toHaveLength(0);
+    });
+
+    it("should recursively remove items", () => {
+      let counter = 0;
+
+      mockedGenerateId.mockImplementation(() => `mockId-${counter++}`);
+
+      const state: Data = {
+        ...defaultData,
+        zones: {
+          zone1: [
+            {
+              type: "Comp",
+              props: { id: "mycomponent", prop: "Some example data" },
+            },
+          ],
+          "mycomponent:zone1": [
+            {
+              type: "Comp",
+              props: { id: "sampleId", prop: "More example data" },
+            },
+          ],
+        },
+      };
+
+      const action: RemoveAction = {
+        type: "remove",
+        index: 0,
+        zone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+
+      expect(newState).toMatchInlineSnapshot(`
+        {
+          "content": [],
+          "root": {
+            "title": "",
+          },
+          "zones": {
+            "zone1": [],
+          },
+        }
+      `);
+    });
+  });
+
+  describe("unregisterZone action", () => {
+    it("should unregister a zone", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: { zone1: [{ type: "Comp", props: { id: "1" } }] },
+      };
+
+      const action: UnregisterZoneAction = {
+        type: "unregisterZone",
+        zone: "zone1",
+      };
+
+      const newState = reducer(state, action);
+      expect(newState.zones?.zone1).toBeUndefined();
+    });
+  });
+
+  describe("registerZone action", () => {
+    it("should register a zone that's been previously unregistered", () => {
+      const state: Data = {
+        ...defaultData,
+        zones: { zone1: [{ type: "Comp", props: { id: "1" } }] },
+      };
+
+      const unregisterAction: UnregisterZoneAction = {
+        type: "unregisterZone",
+        zone: "zone1",
+      };
+
+      const registerAction: RegisterZoneAction = {
+        type: "registerZone",
+        zone: "zone1",
+      };
+
+      const newState = reducer(
+        reducer(state, unregisterAction),
+        registerAction
+      );
+      expect(newState.zones?.zone1[0].props.id).toEqual("1");
+    });
+  });
+
+  describe("set action", () => {
+    it("should set new data", () => {
+      const state: Data = { ...defaultData };
+      const newData: Data = {
+        ...defaultData,
+        root: { title: "Hello, world" },
+        content: [{ type: "Comp", props: { id: "1" } }],
+      };
+
+      const action: SetDataAction = {
+        type: "set",
+        data: newData,
+      };
+
+      const newState = reducer(state, action);
+      expect(newState).toEqual(newData);
+    });
+  });
+});
diff --git a/packages/core/lib/reducer.ts b/packages/core/lib/reducer.ts
index 980062e6c..64a9f946f 100644
--- a/packages/core/lib/reducer.ts
+++ b/packages/core/lib/reducer.ts
@@ -23,34 +23,34 @@ export const addToZoneCache = (key: string, data: Content) => {
   zoneCache[key] = data;
 };
 
-type InsertAction = {
+export type InsertAction = {
   type: "insert";
   componentType: string;
   destinationIndex: number;
   destinationZone: string;
 };
 
-type DuplicateAction = {
+export type DuplicateAction = {
   type: "duplicate";
   sourceIndex: number;
   sourceZone: string;
 };
 
-type ReplaceAction = {
+export type ReplaceAction = {
   type: "replace";
   destinationIndex: number;
   destinationZone: string;
   data: any;
 };
 
-type ReorderAction = {
+export type ReorderAction = {
   type: "reorder";
   sourceIndex: number;
   destinationIndex: number;
   destinationZone: string;
 };
 
-type MoveAction = {
+export type MoveAction = {
   type: "move";
   sourceIndex: number;
   sourceZone: string;
@@ -58,23 +58,23 @@ type MoveAction = {
   destinationZone: string;
 };
 
-type RemoveAction = {
+export type RemoveAction = {
   type: "remove";
   index: number;
   zone: string;
 };
 
-type SetDataAction = {
+export type SetDataAction = {
   type: "set";
   data: Partial<Data>;
 };
 
-type RegisterZoneAction = {
+export type RegisterZoneAction = {
   type: "registerZone";
   zone: string;
 };
 
-type UnregisterZoneAction = {
+export type UnregisterZoneAction = {
   type: "unregisterZone";
   zone: string;
 };