Sliders are a common feature in modern web applications, allowing users to set values within a specified range - like adjusting a price filter, selecting a date, or setting volume levels. While sliders offer a smooth and intuitive experience for users, they can be challenging to automate effectively in UI tests due to their interactive nature.

In this post, we'll explore three powerful methods for automating slider components: drag-and-drop, keyboard-based interactions, and direct value injection. Each approach has unique strengths and limitations, and we'll walk through how to implement them while highlighting which scenarios each method best serves.

Overview of Slider Automation Challenges

Automating sliders can present unique challenges for QA engineers due to the interactive and variable nature of these components. Unlike static elements, sliders require precise movements, accurate value settings, and often respond differently across browsers and devices. Let's look at some common issues encountered when automating sliders:

1. Ensuring Accuracy in Setting Values

Sliders often represent a continuous or range-based scale, making it crucial to set values accurately for testing specific cases. For instance, a slider might allow selecting a value from $10 to $300, and ensuring it lands precisely on a value such as $150 requires precise control. However, small increments, range limits, and the slider's visual positioning make exact value selection challenging. Different browsers may also interpret movements or keyboard inputs slightly differently, which can introduce inconsistencies in automation results.

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Slider Component in Action

2. Handling Browser Differences and Inconsistencies

Sliders are prone to browser-specific quirks that can make automation unpredictable. For example, drag-and-drop actions may work differently in Chrome compared to Firefox, or the way keyboard interactions are handled might vary slightly. Additionally, each browser has its rendering engine, which can influence how the slider responds visually and interactively. Automating sliders across multiple browsers often requires additional handling or adjustments to ensure that actions produce consistent results.

3. Testing Both Desktop and Mobile Behaviors

In a mobile context, sliders are often adjusted using touch gestures, such as swiping or tapping, rather than mouse or keyboard input. Mobile interactions introduce another layer of complexity, as simulating these gestures requires touch-based events. Testing desktop and mobile behaviors may demand separate handling within tests, as a slider automation method that works on a desktop may not translate smoothly to mobile devices. Ensuring compatibility across both platforms is crucial for providing a consistent user experience.

4. Choosing the Right Automation Approach for Specific Needs

Each slider automation approach - drag-and-drop, keyboard-based interactions, and direct value injection - has its strengths and limitations. For instance, while drag-and-drop closely simulates user behavior, it can be imprecise for targeting exact values. Keyboard interactions may offer more control but only work if the slider supports keyboard input. Direct value injection is quick and accurate but bypasses user interactions entirely. Choosing the right method depends on the specific goals of the test, whether it's simulating real user interactions, achieving precise values, or focusing on functionality over UI responsiveness.

Method 1: Drag-and-Drop Actions

The drag-and-drop approach for automating sliders closely mimics real user interactions by using pointer events to move the slider thumb across a defined track. This method allows the test to emulate how a user would click and drag the slider to adjust values, making it especially useful for end-to-end testing. By calculating specific pixel positions, we can direct the slider to particular values along the track.

Pros:

• Realistic User Simulation: Drag-and-drop closely replicates the way users interact with sliders, making it ideal for user simulation.
• UI Responsiveness Testing: This method is useful for testing animations, transitions, and how the UI responds to pointer events.
• End-to-End Interaction Testing: Since it replicates the user's drag action, it's well-suited for end-to-end tests that require full interaction verification.

Cons:

• Precision Challenges: Achieving precise values can be difficult, especially on sliders with a wide range, as it requires pixel-perfect control.
• Browser-Specific Quirks: The drag-and-drop method can be sensitive to differences in how browsers handle pointer events, sometimes requiring adjustments for each browser.

Code example

In the following test, we use Playwright to simulate drag-and-drop actions that move a slider between minimum, midpoint, and maximum values on the range.

The test starts by navigating to the page containing the slider. Be sure to update the URL to point to the correct location of your slider page, whether it's a local file or a hosted URL.

                
test("Drag-and-Drop Actions", async ({ page }) => {
  await page.goto("your-website-url");
                

Next, we select the slider element on the page using its CSS selector, #priceRangeSlider. This slider reference will be used to interact with and retrieve information about the slider in the following steps.

                
const slider = await page.$("#priceRangeSlider");
                

Now, we retrieve the boundingBox of the slider, which provides details about its position and dimensions. We specifically store the startX position and sliderWidth, which we'll use to calculate exact x-coordinates for setting specific slider values.

                
const boundingBox = await slider.boundingBox();
const startX = boundingBox.x;
const sliderWidth = boundingBox.width;
                

We define three target positions based on the slider's starting point (startX) and width:

• minPosition: The leftmost position, representing the minimum slider value (e.g., $10).
• midPosition: The midpoint of the slider width, corresponding to an approximate mid-range value (e.g., ~$155).
• maxPosition: The rightmost end of the slider, representing the maximum value (e.g., $300).

                
const minPosition = startX;
const midPosition = startX + sliderWidth / 2; 
const maxPosition = startX + sliderWidth;
                

To move the slider to the minimum position, we simulate a drag-and-drop action:

• Position the Mouse: Move the mouse to the starting point of the slider.
• Mouse Down: Simulate pressing the mouse button down to grab the slider thumb.
• Drag to Target: Move the mouse to minPosition (the left edge of the slider).
• Mouse Up: Release the mouse button, setting the slider to the minimum value.

Finally, we verify that the slider's displayed value is 10 using an assertion. This checks that our action correctly set the slider to the expected minimum.

                
await page.mouse.move(startX, boundingBox.y + boundingBox.height / 2);
await page.mouse.down();
await page.mouse.move(minPosition, boundingBox.y + boundingBox.height / 2);
await page.mouse.up();
expect(page.locator("#sliderValue")).toHaveText("10");
                

Now, we repeat the same steps to set the slider to the midpoint position:

• Move to Start: Position the mouse back to the starting point of the slider.
• Drag to Midpoint: Move the mouse to the midPosition, approximately halfway along the slider's width.
• Assert Value: We verify that the slider's displayed value is around 155, ensuring that the slider was moved to the correct midpoint position.

                
await page.mouse.move(startX, boundingBox.y + boundingBox.height / 2);
await page.mouse.down();
await page.mouse.move(midPosition, boundingBox.y + boundingBox.height / 2);
await page.mouse.up();
expect(page.locator("#sliderValue")).toHaveText("155");
                

Finally, we move the slider to the maximum position:

• Reposition the Mouse: Start again from the slider's initial position.
• Drag to Max Position: Move to the calculated maxPosition, the far right of the slider.
• Check the Value: The final assertion confirms that the slider displays 300, verifying that the slider has reached its maximum setting.

                
  await page.mouse.move(startX, boundingBox.y + boundingBox.height / 2);
  await page.mouse.down();
  await page.mouse.move(maxPosition, boundingBox.y + boundingBox.height / 2);
  await page.mouse.up();
  expect(page.locator("#sliderValue")).toHaveText("300");
});
                

Best Use Cases

• Visual or UX Testing: Drag-and-drop is ideal for verifying how the slider visually responds to user actions and whether it animates smoothly.
• End-to-End Testing for Real-World Behavior: Since it closely mimics a user's interaction, this approach is well-suited for tests that need to verify complete interaction workflows.

This method provides a high-fidelity simulation of user behavior, making it ideal for scenarios that require a realistic interaction test, particularly where the focus is on the user experience. In cases where precision or efficiency is prioritized, however, alternate methods may offer more control and reliability.

Method 2: Keyboard-Based Interactions

This method uses keyboard events, such as ArrowRight and ArrowLeft, to incrementally adjust the slider's value. It's especially useful for testing accessibility and fine-tuning precise values since many users rely on keyboard navigation, and this method simulates a real-world interaction for them.

Pros:

• Provides precise adjustments, especially for sliders with smaller ranges.
• Supports accessibility testing, as keyboard navigation is a common accessibility requirement.

Cons:

• Slower compared to direct injection since each change requires simulating individual key presses.
• Not all sliders natively support keyboard interactions.

Code example

The test begins by navigating to the URL of the page containing the slider component. Update the URL to point to the correct location of your slider page.

                
test("Keyboard-Based Interactions", async ({ page }) => {
  await page.goto("your-website-url");
                

We select the slider using its #priceRangeSlider ID and set focus to it. This is essential for receiving keyboard events, as only the focused element will respond to key presses in the test.

                
const slider = await page.$("#priceRangeSlider");
await slider.focus();
                

We define a helper function, setSliderValue, to incrementally adjust the slider to the target value. This line retrieves the current value of the slider and stores it in currentValue, which will be used in the upcoming loops to control the slider's movement.

                
async function setSliderValue(targetValue) {
  let currentValue = await page.evaluate((el) => el.value, slider);
                

In this loop, we press ArrowRight to increase the slider value until it reaches the target. After each key press, we retrieve the slider's updated value to check if it matches targetValue. The loop continues until the slider reaches or exceeds targetValue, simulating how a user would interact with it by pressing the right arrow key.

                
while (parseInt(currentValue, 10) < targetValue) {
  await slider.press("ArrowRight");
  currentValue = await page.evaluate((el) => el.value, slider);
}
                

This second loop does the opposite: it presses ArrowLeft to decrease the slider value until it reaches the target. This is useful if we want to move the slider left (to a lower value) and is a crucial part of simulating keyboard-based interactions, where each adjustment relies on an individual key press.

                
while (parseInt(currentValue, 10) > targetValue) {
  await slider.press("ArrowLeft");
  currentValue = await page.evaluate((el) => el.value, slider);
}
                

Finally, we call setSliderValue for several target values (e.g., 10, 50, 150, and 300) to confirm that the slider correctly adjusts to each specified point. Each call is followed by an assertion that checks if the displayed value matches the target value, ensuring the slider responds accurately to keyboard-based control.

                
  await setSliderValue(10);
  await expect(page.locator("#sliderValue")).toHaveText("10");
  await setSliderValue(50);
  await expect(page.locator("#sliderValue")).toHaveText("50");
  await setSliderValue(150);
  await expect(page.locator("#sliderValue")).toHaveText("150");
  await setSliderValue(300);
  await expect(page.locator("#sliderValue")).toHaveText("300");
});
                

Best Use Cases

• Accessibility Testing: Verifies that the slider is navigable via keyboard, aligning with accessibility requirements.
• Precision Testing: Ideal for sliders with small increments where specific values are needed, as each adjustment is done incrementally.

This method is robust for ensuring both precision and accessibility, providing a clear view of how keyboard interaction impacts the slider's usability.

Method 3: Direct Value Injection

This method directly sets the slider's value in the DOM using JavaScript, bypassing any user interaction. By directly updating the slider's internal state, it allows for rapid testing and eliminates the need to go through intermediate steps, such as mouse movements or key presses.

Pros:

• Highly Efficient: Direct injection enables quick value changes without needing to simulate real user actions, making tests faster.
• Stable Against UI Quirks: Since it bypasses animations or rendering issues, this method avoids visual inconsistencies that might impact tests relying on actual interactions.

Cons:

• Limited Simulation: Directly setting the value does not mimic real user behavior, so this method may miss certain UI-related issues.
• Not Ideal for End-to-End Testing: If the goal is to replicate a true user experience, this method falls short because it skips interaction steps.

Code example

The test begins by navigating to the URL of the slider component. Be sure to replace the path with the correct location of your HTML file or hosted website.

                
test("Direct Value Injection", async ({ page }) => {
  await page.goto("your-website-url");
                

We define a helper function, setSliderValueDirectly, which uses page.evaluate() to execute JavaScript in the browser context. Inside evaluate, we locate the slider by its priceRangeSlider ID and set its value directly with slider.value = targetValue. To ensure the display updates, we dispatch an input event on the slider. This approach makes the slider reflect the new value immediately without needing any intermediate interactions.

                
async function setSliderValueDirectly(targetValue) {
  await page.evaluate((targetValue) => {
    const slider = document.getElementById("priceRangeSlider");
    slider.value = targetValue;
    slider.dispatchEvent(new Event("input"));
  }, targetValue);
}
                

In this final segment, we call setSliderValueDirectly with specific target values - 10, 50, 150, and 300 - and verify the slider reflects these values by checking that the text displayed in #sliderValue matches the target value. This approach quickly sets and verifies each value, providing an efficient means to test a range of slider positions without user-like interactions.

                
  await setSliderValueDirectly(10);
  await expect(page.locator("#sliderValue")).toHaveText("10");
                  
  await setSliderValueDirectly(50);
  await expect(page.locator("#sliderValue")).toHaveText("50");
                  
  await setSliderValueDirectly(150);
  await expect(page.locator("#sliderValue")).toHaveText("150");
                  
  await setSliderValueDirectly(300);
  await expect(page.locator("#sliderValue")).toHaveText("300");
});
                

Best Use Cases

• Functional Tests: Ideal for situations where speed is crucial, such as verifying core functionality without the need for user simulation.
• Large-Range Sliders: When testing for specific values across a wide slider range, direct injection offers precision and speed.

Direct value injection is optimal for functional testing scenarios, where efficiency and stability are prioritized over mimicking exact user behavior. This method ensures the slider can reach and display intended values without external influences like UI delays or animation.

Conclusion

Automating slider components can be challenging, as each approach to testing offers unique advantages and trade-offs. Choosing the right method depends on our testing needs - whether we're verifying the core functionality of the slider, focusing on accessibility, or testing the exact user experience. By understanding the strengths and limitations of each approach, we can make informed decisions and select the best method for our specific requirements.

Here's a summary of the methods discussed in this blog post:

For those interested in experimenting with these techniques, the complete code examples and the slider component used for testing are available on our GitHub page. Happy testing!