Add simple build functional test

src/test/groovy/net/fabricmc/loom/BuildUtils.groovy

@@ -87,10 +87,10 @@ publishing {
 """
 }
 
-static String genPropsFile(String mcVersion, String yarnVersion, String loaderVersion, String fabricVersion) {
+static String genPropsFile(String mcVersion, String yarnVersion, String loaderVersion, String fabricVersion, boolean caching = true, boolean parallel = true) {
 	"""
-org.gradle.caching=true
-org.gradle.parallel=true
+org.gradle.caching=$caching
+org.gradle.parallel=$parallel
 
 # Fabric Properties
 # check these on https://fabricmc.net/use
@@ -114,3 +114,62 @@ static String genSettingsFile(String name) {
 rootProject.name = '$name'
 """
 }
+
+static String genModJsonFile() {
+	"""
+{
+  "schemaVersion": 1,
+  "id": "modid",
+  "version": "\${version}",
+
+  "name": "Example Mod",
+  "description": "This is an example description! Tell everyone what your mod is about!",
+  "authors": [
+    "Me!"
+  ],
+  "contact": {
+    "homepage": "https://fabricmc.net/",
+    "sources": "https://github.com/FabricMC/fabric-example-mod"
+  },
+
+  "license": "CC0-1.0",
+
+  "environment": "*",
+  "entrypoints": {
+    "main": [
+      "net.fabricmc.example.ExampleMod"
+    ]
+  },
+  "mixins": [
+    "modid.mixins.json"
+  ],
+
+  "depends": {
+    "fabricloader": ">=0.4.0",
+    "fabric": "*"
+  },
+  "suggests": {
+    "flamingo": "*"
+  }
+}
+"""
+}
+
+static String genModExampleFile() {
+	"""
+package net.fabricmc.example;
+
+import net.fabricmc.api.ModInitializer;
+
+public class ExampleMod implements ModInitializer {
+	@Override
+	public void onInitialize() {
+		// This code runs as soon as Minecraft is in a mod-load-ready state.
+		// However, some things (like resources) may still be uninitialized.
+		// Proceed with mild caution.
+
+		System.out.println("Hello Fabric world!");
+	}
+}
+"""
+}

src/test/groovy/net/fabricmc/loom/SimpleBuildFunctionalTest.groovy

@@ -0,0 +1,61 @@
+package net.fabricmc.loom
+
+import org.gradle.testkit.runner.GradleRunner
+import org.junit.Rule
+import org.junit.rules.TemporaryFolder
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static net.fabricmc.loom.BuildUtils.*
+import static org.gradle.testkit.runner.TaskOutcome.SUCCESS
+
+/**
+ * Created by Mitchell Skaggs on 6/10/2019.
+ */
+class SimpleBuildFunctionalTest extends Specification {
+	@Rule
+	TemporaryFolder testProjectDir = new TemporaryFolder()
+	File settingsFile
+	File buildFile
+	File propsFile
+	File modJsonFile
+	File modExampleFile
+
+	def setup() {
+		settingsFile = testProjectDir.newFile('settings.gradle')
+		buildFile = testProjectDir.newFile('build.gradle')
+		propsFile = testProjectDir.newFile('gradle.properties')
+
+		testProjectDir.newFolder("src", "main", "resources")
+		modJsonFile = testProjectDir.newFile('src/main/resources/fabric.mod.json')
+
+		testProjectDir.newFolder("src", "main", "java", "net", "fabricmc", "example")
+		modExampleFile = testProjectDir.newFile("src/main/java/net/fabricmc/example/ExampleMod.java")
+	}
+
+	@Unroll
+	def "simple build succeeds using Minecraft #mcVersion"() {
+		given:
+		settingsFile << genSettingsFile("simple-build-functional-test")
+		propsFile << genPropsFile(mcVersion, yarnVersion, loaderVersion, fabricVersion)
+		buildFile << genBuildFile()
+		modJsonFile << genModJsonFile()
+		modExampleFile << genModExampleFile()
+
+		when:
+		def result = GradleRunner.create()
+				.withProjectDir(testProjectDir.root)
+				.withArguments('build')
+				.withPluginClasspath()
+				.build()
+
+		then:
+		result.task(":build").outcome == SUCCESS
+
+		where:
+		mcVersion | yarnVersion       | loaderVersion     | fabricVersion
+		'1.14'    | '1.14+build.21'   | '0.4.8+build.155' | '0.3.0+build.184'
+		'1.14.1'  | '1.14.1+build.10' | '0.4.8+build.155' | '0.3.0+build.184'
+		'1.14.2'  | '1.14.2+build.7'  | '0.4.8+build.155' | '0.3.0+build.184'
+	}
+}