diff --git a/app/test/processing/app/AbstractGUITest.java b/app/test/processing/app/AbstractGUITest.java
index 913508856..37f0ebefe 100644
--- a/app/test/processing/app/AbstractGUITest.java
+++ b/app/test/processing/app/AbstractGUITest.java
@@ -60,7 +60,7 @@ public abstract class AbstractGUITest extends AbstractWithPreferencesTest {
     window = GuiActionRunner.execute(new GuiQuery<ArduinoFrameFixture>() {
       @Override
       protected ArduinoFrameFixture executeInEDT() throws Throwable {
-        return new ArduinoFrameFixture(new Base(new String[0]).editors.get(0));
+        return new ArduinoFrameFixture(createBase().editors.get(0));
       }
     });
   }
diff --git a/app/test/processing/app/AbstractWithPreferencesTest.java b/app/test/processing/app/AbstractWithPreferencesTest.java
index 10a690393..0045ee5fc 100644
--- a/app/test/processing/app/AbstractWithPreferencesTest.java
+++ b/app/test/processing/app/AbstractWithPreferencesTest.java
@@ -29,6 +29,7 @@
 
 package processing.app;
 
+import static org.junit.Assert.assertEquals;
 import org.junit.Before;
 import org.junit.After;
 
@@ -47,12 +48,30 @@ public abstract class AbstractWithPreferencesTest {
    * Subclasses can add files here in @Test or @Before functions.
    */
   protected List<File> deleteAfter = new LinkedList<File>();
+  protected File preferencesFile;
 
   @Before
   public void init() throws Exception {
+    File settingsDir = Files.createTempDirectory("arduino_test_settings").toFile();
+    deleteAfter.add(settingsDir);
+
+    preferencesFile = new File(settingsDir, "preferences.txt");
+    File sketchbookDir = new File(settingsDir, "sketchbook");
+    sketchbookDir.mkdir();
+
     BaseNoGui.initPlatform();
     BaseNoGui.getPlatform().init();
-    PreferencesData.init(null);
+
+    PreferencesData.init(preferencesFile);
+    // Do not read anything from e.g. ~/.arduino15
+    PreferencesData.set("settings.path", settingsDir.toString());
+    // Do not read or write the default ~/Arduino sketchbook
+    PreferencesData.set("sketchbook.path", sketchbookDir.toString());
+    // Write the defaults, with these changes to file. This allows them
+    // to be reloaded when creating a Base instance (see getBaseArgs()
+    // below).
+    PreferencesData.save();
+
     Theme.init();
 
     BaseNoGui.initPackages();
@@ -61,6 +80,31 @@ public abstract class AbstractWithPreferencesTest {
     deleteAfter.add(Base.untitledFolder);
   }
 
+  /**
+   * Returns arguments to be passed to the Base constructor or on the
+   * commandline to set up the created dummy environment.
+   */
+  protected String[] getBaseArgs() {
+    return new String[] {
+      // Preferences are loaded (using --preferences-file) before
+      // processing any other commandline options (e.g. --pref), so only
+      // use --preferences-file here. Also, this does not affect the
+      // "action" mode, for tests that require the GUI to be loaded.
+      "--preferences-file", preferencesFile.toString(),
+    };
+  }
+
+  /**
+   * Creates a new instance of Base. Always use this rather than calling
+   * it directly, to ensure the right settings are used.
+   */
+  protected Base createBase() throws Exception {
+    Base base = new Base(getBaseArgs());
+    // Doublecheck that the right preferencesFile was loaded
+    assertEquals(preferencesFile, PreferencesData.preferencesFile);
+    return base;
+  }
+
   @After
   public void cleanup() throws IOException {
     for (File f : deleteAfter)
diff --git a/app/test/processing/app/CommandLineTest.java b/app/test/processing/app/CommandLineTest.java
index ddbc3bada..1db6afe12 100644
--- a/app/test/processing/app/CommandLineTest.java
+++ b/app/test/processing/app/CommandLineTest.java
@@ -45,7 +45,13 @@ import org.junit.Test;
 import processing.app.helpers.OSUtils;
 import processing.app.helpers.PreferencesMap;
 
-public class CommandLineTest {
+/**
+ * This extends AbstractWithPreferencesTest which initializes part of
+ * the internal Arduino structures. Most of that is not required, but it
+ * also conveniently sets up a settings directory and preferences file,
+ * which we can use here (through getBaseArgs()).
+ */
+public class CommandLineTest extends AbstractWithPreferencesTest {
 
   private static File buildPath;
   private static File arduinoPath;
@@ -81,6 +87,7 @@ public class CommandLineTest {
 
     List<String> args = new ArrayList<String>();
     args.add(arduinoPath.getAbsolutePath());
+    args.addAll(Arrays.asList(getBaseArgs()));
     args.addAll(Arrays.asList(extraArgs));
 
     System.out.println("Running: " + String.join(" ", args));
diff --git a/app/test/processing/app/DefaultTargetTest.java b/app/test/processing/app/DefaultTargetTest.java
index 37819c84c..24767bee3 100644
--- a/app/test/processing/app/DefaultTargetTest.java
+++ b/app/test/processing/app/DefaultTargetTest.java
@@ -57,7 +57,7 @@ public class DefaultTargetTest extends AbstractWithPreferencesTest {
     PreferencesData.set("board", "unreal_board");
 
     // should not raise an exception
-    new Base(new String[0]);
+    createBase();
 
     // skip test if no target platforms are available
     Assume.assumeNotNull(BaseNoGui.getTargetPlatform());