diff --git a/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/util/Strings.kt b/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/util/Strings.kt
index e126ae0..c9c1f8a 100644
--- a/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/util/Strings.kt
+++ b/app/src/main/java/net/thauvin/erik/android/tesremoteprogrammer/util/Strings.kt
@@ -18,10 +18,11 @@
 package net.thauvin.erik.android.tesremoteprogrammer.util
 
 import android.text.Html
+import android.text.Spanned
 
 private val digitPattern = Regex("[0-9]+")
 
-fun String.fromHtml() = Html.fromHtml(this, Html.FROM_HTML_MODE_LEGACY)
+fun String.fromHtml(): Spanned = Html.fromHtml(this, Html.FROM_HTML_MODE_LEGACY)
 
 fun String.isDigits() = isNotBlank() && matches(digitPattern)
 
diff --git a/app/src/test/java/net/thauvin/erik/android/tesremoteprogrammer/util/StringsTest.kt b/app/src/test/java/net/thauvin/erik/android/tesremoteprogrammer/util/StringsTest.kt
new file mode 100644
index 0000000..7d4285f
--- /dev/null
+++ b/app/src/test/java/net/thauvin/erik/android/tesremoteprogrammer/util/StringsTest.kt
@@ -0,0 +1,53 @@
+package net.thauvin.erik.android.tesremoteprogrammer.util
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class StringsTest {
+
+    @Test
+    fun isDigits() {
+        assertTrue("0-9", "0123456789".isDigits())
+        assertFalse("a", "a".isDigits())
+        assertFalse("1.3", "1.3".isDigits())
+        assertFalse("empty", "".isDigits())
+        assertFalse("blank", "    ".isDigits())
+    }
+
+    @Test
+    fun isDKS() {
+        assertTrue(Dtmf.DKS.isDKS())
+        assertFalse(Dtmf.LINEAR.isDKS())
+    }
+
+    @Test
+    fun isLinear() {
+        assertTrue(Dtmf.LINEAR.isLinear())
+        assertFalse(Dtmf.DKS.isLinear())
+    }
+
+    @Test
+    fun ifNull() {
+        val n: String? = null
+        assertEquals("null", n.ifNull(), "")
+        assertEquals("test", "test".ifNull(), "test")
+    }
+
+    @Test
+    fun replaceAll() {
+        val s = "This is a test."
+        val r = arrayOf(
+            Pair("i", ""),
+            Pair("is", "no"),
+            Pair("TiT", "no"),
+            Pair("t", "T"),
+            Pair(".", "?"),
+            Pair(" ", "-"),
+            Pair("es", "i")
+        )
+
+        assertEquals(s.replaceAll(r), "Ths-s-a-TiT?")
+    }
+}