Why testing ensures app reliability in Android Kotlin - Build It to Prove It

Build: App Reliability Tester

This screen helps demonstrate how testing ensures app reliability by running a simple test and showing the result.

Target UI

-------------------------
|  App Reliability Tester |
|-----------------------|
| [Run Test]            |
|                       |
| Test Result:          |
|                       |
|                       |
-------------------------

Add a button labeled 'Run Test'.

When the button is tapped, run a simple test function that returns success or failure.

Display the test result below the button as 'Test Passed' or 'Test Failed'.

Use Kotlin and Android best practices.

Ensure the UI updates immediately after the test runs.

Starter Code

Android Kotlin

package com.example.apptester

import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val runTestButton: Button = findViewById(R.id.runTestButton)
        val testResultText: TextView = findViewById(R.id.testResultText)

        // TODO: Add click listener to runTestButton
        // TODO: Run test and update testResultText
    }

    // TODO: Add a simple test function that returns Boolean
}

Task 1

Task 2

Task 3

Task 4

Solution

Android Kotlin

package com.example.apptester

import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val runTestButton: Button = findViewById(R.id.runTestButton)
        val testResultText: TextView = findViewById(R.id.testResultText)

        runTestButton.setOnClickListener {
            val testPassed = runSimpleTest()
            if (testPassed) {
                testResultText.text = "Test Passed"
            } else {
                testResultText.text = "Test Failed"
            }
        }
    }

    private fun runSimpleTest(): Boolean {
        // Simulate a test that checks if 2 + 2 equals 4
        return (2 + 2 == 4)
    }
}

This app screen has a button labeled 'Run Test'. When the user taps it, the app runs a simple test function that checks if 2 + 2 equals 4. This simulates a basic reliability check. The result is shown immediately below the button as 'Test Passed' or 'Test Failed'. This example shows how testing can confirm that parts of the app work as expected, which helps ensure the app is reliable and trustworthy.

Final Result

Completed Screen

-------------------------
|  App Reliability Tester |
|-----------------------|
| [Run Test]            |
|                       |
| Test Result:          |
| Test Passed           |
|                       |
-------------------------

User taps the 'Run Test' button.

The app runs the simple test function.

The text below updates to 'Test Passed' immediately.

Stretch Goal

Add a second test that sometimes fails to show how testing catches errors.

💡 Hint

Create another function that returns false randomly and update the UI to show which test passed or failed.

Practice

1. Why is testing important for mobile apps?

easy

A. It changes the app design automatically

B. It finds problems before users see them

C. It makes the app run faster

D. It removes all bugs without coding

Solution

1. Step 1: Understand the purpose of testing

   Testing helps find errors or bugs early in development before users encounter them.

2. Step 2: Compare options to testing benefits

   Only It finds problems before users see them correctly states that testing finds problems before users see them, which improves app reliability.

3. Final Answer:

   It finds problems before users see them -> Option B

4. Quick Check:

   Testing = Finds problems early [OK]

Hint: Testing catches bugs early to protect users [OK]

Common Mistakes:

• Thinking testing speeds up the app
• Believing testing changes app design
• Assuming testing removes bugs automatically

2. Which Kotlin syntax correctly defines a simple test function?

easy

A. fun testExample() assert(true)

B. test fun example() { assertTrue() }

C. fun exampleTest { assertTrue(true) }

D. fun testExample() { assert(true) }

Solution

1. Step 1: Review Kotlin function syntax

   A function starts with 'fun', followed by name and parentheses, then braces for body.

2. Step 2: Check each option for correct syntax

   fun testExample() { assert(true) } uses correct syntax: 'fun testExample() { assert(true) }'. Others have syntax errors like missing parentheses or wrong order.

3. Final Answer:

   fun testExample() { assert(true) } -> Option D

4. Quick Check:

   Correct Kotlin function syntax = fun testExample() { assert(true) } [OK]

Hint: Look for 'fun name() { }' pattern in Kotlin [OK]

Common Mistakes:

• Omitting parentheses after function name
• Placing 'fun' keyword incorrectly
• Missing braces around function body

3. What will this Kotlin test code print if the app crashes on null input?

fun testNullInput() {
  val input: String? = null
  val result = input!!.length
  println("Test passed")
}

medium

A. NullPointerException error

B. No output

C. 0

D. Test passed

Solution

1. Step 1: Understand the '!!' operator in Kotlin

   The '!!' forces a nullable variable to non-null, throwing NullPointerException if null.

2. Step 2: Analyze the code behavior with null input

   Since input is null, 'input!!' throws NullPointerException before printing anything.

3. Final Answer:

   NullPointerException error -> Option A

4. Quick Check:

   '!!' on null = NullPointerException [OK]

Hint: Remember '!!' crashes if value is null [OK]

Common Mistakes:

• Assuming code prints 'Test passed' anyway
• Thinking null length is zero
• Ignoring exception from '!!' operator

4. This test function is supposed to check if a list is empty, but it fails. What is the error?

fun testEmptyList() {
  val list = listOf<Int>()
  assert(list.isNotEmpty())
}

medium

A. Missing parentheses after listOf

B. Using assert instead of assertTrue

C. Wrong assertion condition for empty list

D. List should be mutable

Solution

1. Step 1: Understand the test goal

   The test wants to check if the list is empty, so it should assert that list is empty.

2. Step 2: Check the assertion condition

   Current code asserts list.isNotEmpty(), which is false for an empty list, causing test failure.

3. Final Answer:

   Wrong assertion condition for empty list -> Option C

4. Quick Check:

   Test empty list = assert(list.isEmpty()) [OK]

Hint: Match assertion to test goal carefully [OK]

Common Mistakes:

• Confusing isEmpty() with isNotEmpty()
• Using wrong assert function
• Thinking listOf needs parentheses fix

5. You want to ensure your app still works after adding a new feature. Which testing approach best helps keep reliability?

hard

A. Write unit tests for existing and new code

B. Only test the new feature manually

C. Skip tests and fix bugs after release

D. Test only on one device model

Solution

1. Step 1: Understand how to keep app reliable after changes

   Testing existing and new code with unit tests helps catch bugs early and ensures features work together.

2. Step 2: Evaluate options for best practice

   Write unit tests for existing and new code covers both existing and new code with automated tests, which is best for reliability.

3. Final Answer:

   Write unit tests for existing and new code -> Option A

4. Quick Check:

   Unit tests for all code = reliability [OK]

Hint: Test all code, not just new parts [OK]

Common Mistakes:

• Testing only new features manually
• Ignoring tests until after release
• Testing on limited devices only