Add tests

jib-core/src/main/java/com/google/cloud/tools/jib/frontend/JavaEntrypointConstructor.java

@@ -30,7 +30,8 @@ public class JavaEntrypointConstructor {
 
   public static List<String> makeDefaultEntrypoint(
       String appRoot, List<String> jvmFlags, String mainClass) {
-    Preconditions.checkArgument(appRoot.startsWith("/"));
+    Preconditions.checkArgument(
+        appRoot.startsWith("/"), "appRoot should be an absolute path in Unix-style");
     appRoot = appRoot.endsWith("/") ? appRoot : appRoot + '/';
 
     return makeEntrypoint(

jib-core/src/main/java/com/google/cloud/tools/jib/frontend/JavaLayerConfigurations.java

@@ -165,8 +165,8 @@ private JavaLayerConfigurations(
   }
 
   /**
-   * Returns the Unix-style, absolute path for the application root in the container image. May or
-   * may not end with a trailing forward slash ('/').
+   * Returns the Unix-style, absolute path for the application root in the container image. The path
+   * may or may not end with a forward slash ('/').
    *
    * @return Unix-style, absolute path for the application root
    */

jib-core/src/test/java/com/google/cloud/tools/jib/frontend/JavaEntrypointConstructorTest.java

@@ -16,7 +16,9 @@
 
 package com.google.cloud.tools.jib.frontend;
 
+import com.google.cloud.tools.jib.configuration.ContainerConfiguration;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import org.junit.Assert;
 import org.junit.Test;
@@ -54,6 +56,63 @@ public void testMakeEntrypoint() {
         entrypoint);
   }
 
+  @Test
+  public void testMakeDefaultEntrypoint_classpathString() {
+    // Checks that this is also the default entrypoint.
+    List<String> entrypoint = JavaEntrypointConstructor.makeDefaultEntrypoint(
+        ContainerConfiguration.DEFAULT_APP_ROOT, Collections.emptyList(), "someMainClass");
+    Assert.assertEquals("/app/resources/:/app/classes/:/app/libs/*", entrypoint.get(2));
+  }
+
+  @Test
+  public void testMakeDefaultEntrypoint_classpathStringWithNonDefaultAppRoot() {
+    // Checks that this is also the default entrypoint.
+    List<String> entrypoint = JavaEntrypointConstructor.makeDefaultEntrypoint(
+        "/my/app", Collections.emptyList(), "someMainClass");
+    Assert.assertEquals("/my/app/resources/:/my/app/classes/:/my/app/libs/*", entrypoint.get(2));
+  }
+
+  @Test
+  public void testMakeDefaultEntrypoint_appRootWithTrailingSlash() {
+    // Checks that this is also the default entrypoint.
+    List<String> entrypoint = JavaEntrypointConstructor.makeDefaultEntrypoint(
+        "/my/root/", Collections.emptyList(), "SomeMainClass");
+    Assert.assertEquals("/my/root/resources/:/my/root/classes/:/my/root/libs/*", entrypoint.get(2));
+  }
+
+  @Test
+  public void testMakeDefaultEntrypoint_nonAbsoluteAppRoot() {
+    try {
+      JavaEntrypointConstructor.makeDefaultEntrypoint(
+          "relative/path", Collections.emptyList(), "MainClass");
+      Assert.fail();
+    } catch (IllegalArgumentException ex) {
+      Assert.assertEquals("appRoot should be an absolute path in Unix-style", ex.getMessage());
+    }
+  }
+
+  @Test
+  public void testMakeDefaultEntrypoint_windowsAppRootPath() {
+    try {
+      JavaEntrypointConstructor.makeDefaultEntrypoint(
+          "\\windows\\path", Collections.emptyList(), "MyMain");
+      Assert.fail();
+    } catch (IllegalArgumentException ex) {
+      Assert.assertEquals("appRoot should be an absolute path in Unix-style", ex.getMessage());
+    }
+  }
+
+  @Test
+  public void testMakeDefaultEntrypoint_windowsPathWithDriveLetter() {
+    try {
+      JavaEntrypointConstructor.makeDefaultEntrypoint(
+          "D:\\windows\\path", Collections.emptyList(), "MyMain");
+      Assert.fail();
+    } catch (IllegalArgumentException ex) {
+      Assert.assertEquals("appRoot should be an absolute path in Unix-style", ex.getMessage());
+    }
+  }
+
   @Test
   public void testMakeDistrolessJettyEntrypoint() {
     List<String> expected = Arrays.asList("java", "-jar", "/jetty/start.jar");