Set .mill-jvm-version for Mockito tests

Author: ajaychandran

example/migrating/javalib/5-gradle-incomplete/build.mill

@@ -4,7 +4,9 @@
 
 > git init .
 > git remote add -f origin https://github.com/mockito/mockito.git
-> git checkout v5.19.0 # multi-module Java project that requires Java 17+
+> git checkout v5.19.0 # multi-module Java project that requires Java 11
+
+> echo "17" > .mill-jvm-version # Gradle version in use requires Java 17
 
 > ./mill init # imported modules are not fully functional
 converting Gradle build

integration/manual/migrating-gradle/src/MillInitMockitoTests.scala

@@ -14,10 +14,13 @@ object MillInitMockitoTests extends GitRepoIntegrationTestSuite {
     test - integrationTest { tester =>
       import tester.*
 
+      // project requires Java 11 but Gradle version in use requires Java 17
+      os.write(workspacePath / ".mill-jvm-version", "17")
+
       eval("init", stdout = os.Inherit, stderr = os.Inherit).isSuccess ==> true
       eval(("resolve", "_"), stdout = os.Inherit, stderr = os.Inherit).isSuccess ==> true
 
-      // requires support for Java modules
+      // requires javacOptions for Java modules
       eval("mockito-core.compile", stdout = os.Inherit, stderr = os.Inherit).isSuccess ==> false
     }
   }