Add unit tests for String.replace(Map<String, String>) extension

app/build.gradle

@@ -290,6 +290,8 @@ dependencies {
     implementation libs.mozilla.ui.tabcounter
     implementation libs.mozilla.ui.widgets
 
+    testImplementation libs.junit
+
     androidTestImplementation libs.androidx.test.espresso.core
     androidTestImplementation libs.androidx.test.espresso.idling.resources
     constraints {

app/src/test/java/org/mozilla/reference/browser/ext/StringKtTest.kt

@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.reference.browser.ext
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class StringKtTest {
+    @Test
+    fun `replace should replace all keys with their corresponding values`() {
+        val input = "The quick brown fox jumps over the lazy dog"
+        val pairs = mapOf(
+            "quick" to "slow",
+            "brown" to "red",
+            "fox" to "cat",
+            "dog" to "mouse",
+        )
+
+        val result = input.replace(pairs)
+
+        assertEquals("The slow red cat jumps over the lazy mouse", result)
+    }
+
+    @Test
+    fun `replace should return the same string if the map is empty`() {
+        val input = "Hello world"
+        val pairs = emptyMap<String, String>()
+
+        val result = input.replace(pairs)
+
+        assertEquals(input, result)
+    }
+
+    @Test
+    fun `replace should handle keys that are not present in the string`() {
+        val input = "Hello world"
+        val pairs = mapOf("foo" to "bar")
+
+        val result = input.replace(pairs)
+
+        assertEquals("Hello world", result)
+    }
+}