[Uptime] Clear selectedFilters state when action payload is blank (e…

…lastic#99851)

* Clear `selectedFilters` state when action payload is blank.

* Add tests.

* Fix import error.

x-pack/plugins/uptime/public/state/reducers/selected_filters.test.ts

@@ -0,0 +1,76 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+import { selectedFiltersReducer } from './selected_filters';
+import {
+  getSelectedFilters,
+  setSelectedFilters,
+  SelectedFilters,
+} from '../actions/selected_filters';
+import { createAction } from 'redux-actions';
+
+describe('selectedFiltersReducer', () => {
+  let state: SelectedFilters;
+
+  beforeEach(() => {
+    state = {
+      locations: [],
+      ports: [],
+      schemes: ['http'],
+      tags: [],
+    };
+  });
+
+  it('returns state by default', () => {
+    expect(selectedFiltersReducer(state, createAction<void>('fake action')())).toEqual(state);
+  });
+
+  describe('setSelectedFilters', () => {
+    it('returns null for null payload', () => {
+      expect(selectedFiltersReducer(state, setSelectedFilters(null))).toBeNull();
+    });
+
+    it('sets state to the action payload if state is null', () => {
+      expect(
+        selectedFiltersReducer(
+          null,
+          setSelectedFilters({
+            locations: [],
+            ports: [5601],
+            schemes: [],
+            tags: [],
+          })
+        )
+      ).toEqual({ locations: [], ports: [5601], schemes: [], tags: [] });
+    });
+
+    it('merges state and action payload', () => {
+      expect(
+        selectedFiltersReducer(
+          {
+            locations: [],
+            ports: [],
+            schemes: [],
+            tags: [],
+          },
+          setSelectedFilters({
+            locations: [],
+            ports: [5601],
+            schemes: [],
+            tags: ['prod'],
+          })
+        )
+      ).toEqual({ locations: [], ports: [5601], schemes: [], tags: ['prod'] });
+    });
+  });
+
+  describe('getSelectedFilters', () => {
+    it('returns the state', () => {
+      expect(selectedFiltersReducer(state, getSelectedFilters())).toEqual(state);
+    });
+  });
+});

x-pack/plugins/uptime/public/state/reducers/selected_filters.ts

@@ -19,14 +19,12 @@ export function selectedFiltersReducer(
   action: Action<any>
 ): SelectedFilters | null {
   switch (action.type) {
-    case String(getSelectedFilters):
-      return state;
     case String(setSelectedFilters):
-      if (state === null) return { ...action.payload };
+      if (action.payload === null) return null;
       return {
-        ...(state || {}),
         ...action.payload,
       };
+    case String(getSelectedFilters):
     default:
       return state;
   }