diff --git a/src/routePlanner/reducer.test.ts b/src/routePlanner/reducer.test.ts
new file mode 100644
index 0000000..b5cbc19
--- /dev/null
+++ b/src/routePlanner/reducer.test.ts
@@ -0,0 +1,258 @@
+import t from 'tap';
+import { Marker, ReducerAction } from './types';
+import { createChangeStateMethods, markersReducer } from './reducer.js';
+
+const createReducerWithState = () => {
+    let markers: Marker[] = [];
+
+    const changeStateMethods = createChangeStateMethods((action) => {
+        markers = markersReducer(markers, action);
+    });
+
+    return {
+        ...changeStateMethods,
+        getMarkers: () => markers,
+    };
+};
+
+const coordinates1 = { lat: 1, lng: 101 };
+const coordinates2 = { lat: 2, lng: 102 };
+const coordinates3 = { lat: 3, lng: 103 };
+const coordinates4 = { lat: 4, lng: 104 };
+const coordinates5 = { lat: 5, lng: 105 };
+
+const createReducersWithFivePoints = () => {
+    const result = createReducerWithState();
+    result.addMarker(coordinates1);
+    result.addMarker(coordinates2);
+    result.addMarker(coordinates3);
+    result.addMarker(coordinates4);
+    result.addMarker(coordinates5);
+    return result;
+};
+
+const markerPattern = {
+    key: String,
+    moveUp: Function,
+    moveDown: Function,
+    remove: Function,
+};
+
+void t.test('reducer', (t) => {
+    void t.test('throws an error for incorrect action type', (t) => {
+        // just to get to 100% coverage
+        t.throws(() =>
+            markersReducer([], { type: 'unknown' } as unknown as ReducerAction),
+        );
+        t.end();
+    });
+    t.end();
+});
+
+void t.test('reducer methods', (t) => {
+    void t.test('create markers with correct labels', (t) => {
+        const reducers = createReducersWithFivePoints();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('remove first marker', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[0]?.remove();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates2 },
+            { ...markerPattern, label: '2', coordinates: coordinates3 },
+            { ...markerPattern, label: '3', coordinates: coordinates4 },
+            { ...markerPattern, label: '4', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('remove middle marker', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[2]?.remove();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates4 },
+            { ...markerPattern, label: '4', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('remove last marker', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[4]?.remove();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+        ]);
+        t.end();
+    });
+
+    void t.test('do not move first marker up', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[0]?.moveUp();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move first marker down', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[0]?.moveDown();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates2 },
+            { ...markerPattern, label: '2', coordinates: coordinates1 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move second marker up', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[1]?.moveUp();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates2 },
+            { ...markerPattern, label: '2', coordinates: coordinates1 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move second marker down', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[1]?.moveDown();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates3 },
+            { ...markerPattern, label: '3', coordinates: coordinates2 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move middle marker up', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[2]?.moveUp();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates3 },
+            { ...markerPattern, label: '3', coordinates: coordinates2 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move middle marker down', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[2]?.moveDown();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates4 },
+            { ...markerPattern, label: '4', coordinates: coordinates3 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move penultimate marker up', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[3]?.moveUp();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates4 },
+            { ...markerPattern, label: '4', coordinates: coordinates3 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move penultimate marker down', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[3]?.moveDown();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates5 },
+            { ...markerPattern, label: '5', coordinates: coordinates4 },
+        ]);
+        t.end();
+    });
+
+    void t.test('move last marker up', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[4]?.moveUp();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates5 },
+            { ...markerPattern, label: '5', coordinates: coordinates4 },
+        ]);
+        t.end();
+    });
+
+    void t.test('do not move last marker down', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.getMarkers()[4]?.moveDown();
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates2 },
+            { ...markerPattern, label: '3', coordinates: coordinates3 },
+            { ...markerPattern, label: '4', coordinates: coordinates4 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('drag second marker to fourth', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.reorderMarkers({ oldIndex: 1, newIndex: 3 });
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates3 },
+            { ...markerPattern, label: '3', coordinates: coordinates4 },
+            { ...markerPattern, label: '4', coordinates: coordinates2 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    void t.test('drag fourth marker to second', (t) => {
+        const reducers = createReducersWithFivePoints();
+        reducers.reorderMarkers({ oldIndex: 3, newIndex: 1 });
+        t.matchOnlyStrict(reducers.getMarkers(), [
+            { ...markerPattern, label: '1', coordinates: coordinates1 },
+            { ...markerPattern, label: '2', coordinates: coordinates4 },
+            { ...markerPattern, label: '3', coordinates: coordinates2 },
+            { ...markerPattern, label: '4', coordinates: coordinates3 },
+            { ...markerPattern, label: '5', coordinates: coordinates5 },
+        ]);
+        t.end();
+    });
+
+    t.end();
+});
diff --git a/src/routePlanner/reducer.ts b/src/routePlanner/reducer.ts
index 29e5638..4533c04 100644
--- a/src/routePlanner/reducer.ts
+++ b/src/routePlanner/reducer.ts
@@ -1,8 +1,8 @@
 import { nanoid } from 'nanoid';
-import { Marker, ReducerAction, ReorderMarkersParams } from './types';
-import { reorderElements } from '../shared/collections';
 import { Dispatch } from 'preact/hooks';
+import { reorderElements } from '../shared/collections.js';
 import { Coordinates } from '../shared/types';
+import { Marker, ReducerAction, ReorderMarkersParams } from './types';
 
 const reindexMarkers = (markers: Marker[]) =>
     markers.map((marker, i) => {
diff --git a/src/shared/collections.test.ts b/src/shared/collections.test.ts
index 1d2fd37..2a59454 100644
--- a/src/shared/collections.test.ts
+++ b/src/shared/collections.test.ts
@@ -7,7 +7,7 @@ void t.test('reorderElements', (t) => {
         newIndex: number,
         expected: string,
     ) => {
-        t.match(
+        t.matchOnlyStrict(
             reorderElements('abcde'.split(''), oldIndex, newIndex),
             expected.split(''),
         );
diff --git a/src/shared/types.ts b/src/shared/types.ts
index ce5eba8..7593e6f 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -1,6 +1,7 @@
-import type { LatLng } from 'leaflet';
-
-export type Coordinates = LatLng;
+export type Coordinates = {
+    lat: number;
+    lng: number;
+};
 
 export type Waypoint = {
     coordinates: Coordinates;