Add some tests

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

src/utils/AnimationUtils.ts

@@ -14,6 +14,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
+import { clamp } from "lodash";
+
 /**
  * This method linearly interpolates between two points (start, end). This is
  * most commonly used to find a point some fraction of the way along a line
@@ -25,5 +27,6 @@ limitations under the License.
  * @returns
  */
 export function lerp(start: number, end: number, amt: number) {
+    amt = clamp(amt, 0, 1);
     return (1 - amt) * start + amt * end;
 }

test/utils/AnimationUtils-test.ts

@@ -0,0 +1,35 @@
+/*
+Copyright 2021 Šimon Brandner <simon.bra.ag@gmail.com>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { lerp } from "../../src/utils/AnimationUtils";
+
+describe("lerp", () => {
+    it("correctly interpolates", () => {
+        expect(lerp(0, 100, 0.5)).toBe(50);
+        expect(lerp(50, 100, 0.5)).toBe(75);
+        expect(lerp(0, 1, 0.1)).toBe(0.1);
+    });
+
+    it("clamps the interpolant", () => {
+        expect(lerp(0, 100, 50)).toBe(100);
+        expect(lerp(0, 100, -50)).toBe(0);
+    });
+
+    it("handles negative numbers", () => {
+        expect(lerp(-100, 0, 0.5)).toBe(-50);
+        expect(lerp(100, -100, 0.5)).toBe(0);
+    });
+});