Test NoteMapper helper with JUnit 5/Jupiter.

Needs some additional plugins, because Google isn't moving on JUnit 5 support
see
- Google tracking issue:
  android/android-test#224
- Android <-> JUnit 5 plugin
  https://github.com/mannodermaus/android-junit5
- StackOverflow answer about the plugin
  https://stackoverflow.com/questions/46161113/junit-5-for-android-testing

app/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: 'com.android.application'
+apply plugin: 'de.mannodermaus.android-junit5'
 
 android {
     compileSdkVersion 33
@@ -51,6 +52,8 @@ dependencies {
     implementation 'com.google.android.material:material:1.8.0'
     implementation 'androidx.preference:preference:1.2.0'
     implementation "androidx.annotation:annotation:1.6.0"
+
+    testImplementation "org.junit.jupiter:junit-jupiter:5.9.2"
 }
 
 // Not sure why this started happening all of a sudden, but the buidl was failing

app/src/test/java/com/nicobrailo/pianoli/melodies/NoteMapperTest.java

@@ -0,0 +1,41 @@
+package com.nicobrailo.pianoli.melodies;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+import static com.nicobrailo.pianoli.melodies.NoteMapper.get_key_idx_from_note;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+class NoteMapperTest {
+
+    @Test
+    public void noteRangeLimits() {
+        assertEquals(0, get_key_idx_from_note("C1"),
+                "lowest parsable note should be parsed");
+        assertEquals(26, get_key_idx_from_note("B2"),
+                "lowest parsable note should be parsed");
+
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"C#1", "Db1", "D♭1"})
+    public void fancySynonyms(String note) {
+        assertEquals(1, get_key_idx_from_note(note),
+                "all synonyms for the same note should work, including fancy symbols");
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"", " ", "fooooooo"})
+    public void noNoteFallback(String notANote) {
+        assertEquals(5, get_key_idx_from_note(notANote),
+                "non-existing notes should fall back to the not-a-note special value");
+    }
+
+    @Test
+    public void nullSafe() {
+        assertEquals(5, get_key_idx_from_note(null),
+                "Notemapper should gracefully handle null");
+    }
+}

build.gradle

@@ -8,6 +8,7 @@ buildscript {
 
     dependencies {
         classpath 'com.android.tools.build:gradle:7.4.2'
+        classpath "de.mannodermaus.gradle.plugins:android-junit5:1.9.3.0"
 
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files