Add a unit test for DnsConfig.intToInetString

adds JUnit dependencies and basic gradle support to run unit tests,
and a test for DnsConfig.intToInetString().

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

Makefile

@@ -53,7 +53,7 @@ endif
 $(DEBUG_APK): toolchain
 	mkdir -p android/libs
 	go run gioui.org/cmd/gogio -buildmode archive -target android -appid $(APPID) -tags novulkan -o $(AAR) github.com/tailscale/tailscale-android/cmd/tailscale
-	(cd android && ./gradlew assemblePlayDebug)
+	(cd android && ./gradlew test assemblePlayDebug)
 	mv android/build/outputs/apk/play/debug/android-play-debug.apk $@
 
 rundebug: $(DEBUG_APK)
@@ -66,7 +66,7 @@ rundebug: $(DEBUG_APK)
 tailscale-fdroid.apk: toolchain
 	mkdir -p android/libs
 	go run gioui.org/cmd/gogio -buildmode archive -target android -appid $(APPID) -tags novulkan -o $(AAR) github.com/tailscale/tailscale-android/cmd/tailscale
-	(cd android && ./gradlew assembleFdroidDebug)
+	(cd android && ./gradlew test assembleFdroidDebug)
 	mv android/build/outputs/apk/fdroid/debug/android-fdroid-debug.apk $@
 
 # This target is also used by the F-Droid builder.
@@ -76,7 +76,7 @@ release_aar:
 	go run gioui.org/cmd/gogio -ldflags "-X tailscale.com/version.Long=$(VERSIONNAME) -X tailscale.com/version.Short=$(VERSIONNAME_SHORT) -X tailscale.com/version.GitCommit=$(TAILSCALE_COMMIT) -X tailscale.com/version.ExtraGitCommit=$(OUR_VERSION)" -buildmode archive -target android -appid $(APPID) -tags novulkan -o $(AAR) github.com/tailscale/tailscale-android/cmd/tailscale
 
 $(RELEASE_AAB): release_aar
-	(cd android && ./gradlew bundlePlayRelease)
+	(cd android && ./gradlew test bundlePlayRelease)
 	mv ./android/build/outputs/bundle/playRelease/android-play-release.aab $@
 
 release: $(RELEASE_AAB)

android/build.gradle

@@ -50,6 +50,7 @@ dependencies {
 	implementation "androidx.browser:browser:1.2.0"
 	implementation "androidx.security:security-crypto:1.1.0-alpha03"
 	implementation ':ipn@aar'
+	testCompile "junit:junit:4.12"
 
 	// Non-free dependencies.
 	playImplementation 'com.google.android.gms:play-services-auth:18.0.0'

android/src/main/java/com/tailscale/ipn/DnsConfig.java

@@ -229,7 +229,7 @@ public class DnsConfig {
 	}
 
 
-	String intToInetString(int hostAddress) {
+	public String intToInetString(int hostAddress) {
 		return String.format(java.util.Locale.ROOT, "%d.%d.%d.%d",
 			(0xff & hostAddress),
 			(0xff & (hostAddress >> 8)),

android/src/test/java/com/tailscale/ipn/DnsConfigTest.java

@@ -0,0 +1,21 @@
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import com.tailscale.ipn.DnsConfig;
+
+public class DnsConfigTest {
+	DnsConfig dns;
+
+	@Before
+	public void setup() {
+		dns = new DnsConfig(null);
+	}
+
+	@Test
+	public void dnsConfig_intToInetStringTest() {
+		assertEquals(dns.intToInetString(0x0101a8c0), "192.168.1.1");
+		assertEquals(dns.intToInetString(0x04030201), "1.2.3.4");
+		assertEquals(dns.intToInetString(0), "0.0.0.0");
+	}
+}