feat: tests for the debounce util function

Author: andreishket

vis/test/utils/debounce.test.ts

@@ -0,0 +1,131 @@
+import { describe, it, expect, vi } from "vitest";
+import debounce from "../../js/utils/debounce";
+
+describe("Debounce function", () => {
+  const getDelayTimeouts = () => {
+    const BASE_DELAY = 100;
+    const DELAY_WITH_TIMEOUT = BASE_DELAY + 50;
+    const TIMEOUT_BELOW_BASE_DELAY = BASE_DELAY - 50;
+
+    return { BASE_DELAY, DELAY_WITH_TIMEOUT, TIMEOUT_BELOW_BASE_DELAY };
+  };
+
+  it("Should call a callback after delay timeout", async () => {
+    // Getting delay values
+    const { BASE_DELAY, DELAY_WITH_TIMEOUT } = getDelayTimeouts();
+
+    // Mocking callback function to check
+    // how many times it would be called
+    const mockFunc = vi.fn();
+
+    // Create debounced function
+    const debouncedFunc = debounce(mockFunc, BASE_DELAY, false);
+
+    // Call function two times (without delay)
+    debouncedFunc();
+    debouncedFunc();
+
+    // Check that function was not called immediately
+    expect(mockFunc).not.toHaveBeenCalled();
+
+    // Waiting more then delay was configured
+    await new Promise((resolve) => setTimeout(resolve, DELAY_WITH_TIMEOUT));
+
+    // Check that mocked callback function was called once
+    expect(mockFunc).toHaveBeenCalledTimes(1);
+  });
+
+  it("Callback function must be called immediately if immediate is true", async () => {
+    // Getting delay values
+    const { BASE_DELAY, DELAY_WITH_TIMEOUT } = getDelayTimeouts();
+
+    // Mocking callback function to check
+    // how many times it would be called
+    const mockFunc = vi.fn();
+
+    // Create debounced function
+    const debouncedFunc = debounce(mockFunc, BASE_DELAY, true);
+
+    // Call function
+    debouncedFunc();
+
+    // Check that function was called immediately
+    expect(mockFunc).toHaveBeenCalledTimes(1);
+
+    // Waiting more then delay was configured
+    await new Promise((resolve) => setTimeout(resolve, DELAY_WITH_TIMEOUT));
+
+    // Check that mocked callback function was called once
+    expect(mockFunc).toHaveBeenCalledTimes(1);
+  });
+
+  it("Callback function should be called during a delay time", async () => {
+    // Getting delay values
+    const { BASE_DELAY, TIMEOUT_BELOW_BASE_DELAY } = getDelayTimeouts();
+
+    // Mocking callback function to check
+    // how many times it would be called
+    const mockFunc = vi.fn();
+
+    // Create debounced function
+    const debouncedFunc = debounce(mockFunc, BASE_DELAY, false);
+
+    // Call function two times (without delay)
+    debouncedFunc();
+    debouncedFunc();
+
+    //  Waiting less the delay was configured
+    await new Promise((resolve) =>
+      setTimeout(resolve, TIMEOUT_BELOW_BASE_DELAY)
+    );
+
+    // Check that mocked callback function was NOT called
+    expect(mockFunc).not.toHaveBeenCalled();
+
+    //  Waiting until the end of delay
+    await new Promise((resolve) => setTimeout(resolve, BASE_DELAY));
+
+    // Check that mocked callback function was called once
+    expect(mockFunc).toHaveBeenCalledTimes(1);
+  });
+
+  it("Maintaining the context of this", async () => {
+    // Getting delay values
+    const { BASE_DELAY, DELAY_WITH_TIMEOUT } = getDelayTimeouts();
+
+    // Defining context value
+    const VALUE = 5;
+
+    // Mock object to test that this is working correctly
+    const MOCK_OBJECT_WITH_CONTEXT = { value: VALUE };
+
+    // Mocking callback function to check
+    // how many times it would be called
+    const mockFunc = vi.fn(function () {
+      // @ts-ignore
+      return this.value;
+    });
+
+    // Create debounced function
+    const debouncedFunc = debounce(
+      mockFunc.bind(MOCK_OBJECT_WITH_CONTEXT),
+      BASE_DELAY,
+      false
+    );
+
+    // Calling function once
+    debouncedFunc();
+
+    // Function must not been called
+    expect(mockFunc).not.toHaveBeenCalled();
+
+    // Waiting until the end of delay
+    await new Promise((resolve) => setTimeout(resolve, DELAY_WITH_TIMEOUT));
+
+    // Check that callback function was called once
+    expect(mockFunc).toHaveBeenCalledTimes(1);
+
+    // Check that callback function was called with correct context
+    expect(mockFunc).toHaveReturnedWith(VALUE);
+  });
+});