Respect JAVA_HOME environment variable (#69)

* Respect JAVA_HOME

Closes #26

* Prioritize JAVA_HOME before java.home

Author: andreoss

pom.xml

@@ -106,6 +106,12 @@
       <version>${junit.version}</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>com.github.stefanbirkner</groupId>
+      <artifactId>system-rules</artifactId>
+      <version>1.19.0</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
 
   <build>

src/main/java/org/scalatest/tools/maven/MojoUtils.java

@@ -1,9 +1,8 @@
 package org.scalatest.tools.maven;
 
-import java.util.Collections;
-import java.util.List;
-import java.util.ArrayList;
 import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
 
 import static org.apache.commons.lang3.StringUtils.isEmpty;
 
@@ -126,11 +125,26 @@ static String[] concat(List<String>...lists){
         return c.toArray(new String[c.size()]);
     }
 
+    private static String getJavaHome() {
+        final String result;
+        if (!isEmpty(System.getenv("JAVA_HOME"))) {
+            result = System.getenv("JAVA_HOME");
+        } else if (!isEmpty(System.getProperty("java.home"))) {
+            result = System.getProperty("java.home");
+        } else {
+            result = null;
+        }
+        return result;
+    }
+
     static String getJvm() {
-        if (!isEmpty(System.getProperty( "java.home" ))) {
-            return System.getProperty( "java.home" ) + File.separator + "bin" + File.separator + "java";
+        final String jh = getJavaHome();
+        final String result;
+        if (jh == null) {
+            result = "java";
         } else {
-            return "java";
+            result = jh + File.separator + "bin" + File.separator + "java";
         }
+        return result;
     }
 }

src/test/scala/org/scalatest/tools/maven/MojoUtilsTest.scala

@@ -1,32 +1,43 @@
 package org.scalatest.tools.maven
 
-import org.junit.{After, Before, Test}
+import org.junit.contrib.java.lang.system.{ClearSystemProperties, EnvironmentVariables}
+import org.junit.{Rule, Test}
 
 class MojoUtilsTest {
-  private var savedJavaHome: Option[String] = _
+  val _env: EnvironmentVariables = new EnvironmentVariables()
+  val _sys: ClearSystemProperties = new ClearSystemProperties("java.home")
 
-  @Before
-  def save(): Unit = {
-    savedJavaHome = Option(System.getProperty("java.home"))
-  }
+  @Rule
+  def env: EnvironmentVariables = _env
 
-  @After
-  def restore(): Unit = {
-    savedJavaHome match {
-      case None => System.clearProperty("java.home")
-      case Some(value) => System.setProperty("java.home", value)
-    }
-  }
+  @Rule
+  def sys: ClearSystemProperties = _sys
 
   @Test
   def getJvmHappyPath(): Unit = {
+    env.clear("JAVA_HOME")
     System.setProperty("java.home", "/test/jvm")
     assert(MojoUtils.getJvm == "/test/jvm/bin/java")
   }
 
   @Test
   def getJvmWithoutJavaHome(): Unit = {
-    System.clearProperty("java.home")
+    env.clear("JAVA_HOME")
     assert(MojoUtils.getJvm == "java")
   }
+
+  @Test
+  def getJvmFromEnvironment(): Unit = {
+    env.clear("JAVA_HOME")
+    env.set("JAVA_HOME", "/opt/jdk-11")
+    Console.print(MojoUtils.getJvm)
+    assert(MojoUtils.getJvm == "/opt/jdk-11/bin/java")
+  }
+
+  @Test
+  def getJvmJavaHomeIsPriority(): Unit = {
+    System.setProperty("java.home", "/test/jvm")
+    env.set("JAVA_HOME", "/opt/jdk-11")
+    assert(MojoUtils.getJvm == "/opt/jdk-11/bin/java")
+  }
 }