Following accepted answer for question regarding how to init runscript from resources folder: problem with INIT=RUNSCRIPT and relative paths.
Connection String:
jdbc:h2:mem:;INIT=RUNSCRIPT FROM 'classpath:desktop/core/database/databaseCreation.sql'
However i get exception that file is not found even when file is present.
Exception:
org.h2.jdbc.JdbcSQLNonTransientException: IO Exception: "java.io.FileNotFoundException: resource /desktop/core/database/databaseCreation.sql"; "classpath:desktop/core/database/databaseCreation.sql"; SQL statement:
RUNSCRIPT FROM 'classpath:desktop/core/database/databaseCreation.sql' [90031-210]
    at com.h2database@2.1.210/org.h2.message.DbException.getJdbcSQLException(DbException.java:573)
    at com.h2database@2.1.210/org.h2.message.DbException.getJdbcSQLException(DbException.java:496)
    at com.h2database@2.1.210/org.h2.message.DbException.get(DbException.java:216)
    at com.h2database@2.1.210/org.h2.message.DbException.convertIOException(DbException.java:461)
    at com.h2database@2.1.210/org.h2.command.dml.ScriptBase.openInput(ScriptBase.java:168)
    at com.h2database@2.1.210/org.h2.command.dml.RunScriptCommand.update(RunScriptCommand.java:52)
    at com.h2database@2.1.210/org.h2.command.CommandContainer.update(CommandContainer.java:174)
    at com.h2database@2.1.210/org.h2.command.Command.executeUpdate(Command.java:252)
    at com.h2database@2.1.210/org.h2.engine.Engine.openSession(Engine.java:279)
    at com.h2database@2.1.210/org.h2.engine.Engine.createSession(Engine.java:201)
    at com.h2database@2.1.210/org.h2.engine.SessionRemote.connectEmbeddedOrServer(SessionRemote.java:338)
    at com.h2database@2.1.210/org.h2.jdbc.JdbcConnection.<init>(JdbcConnection.java:122)
    at com.h2database@2.1.210/org.h2.Driver.connect(Driver.java:59)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:681)
    at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:252)
    at ispfdesktop/desktop.core.database.DatabaseManager.connectToInMemoryDatabase(DatabaseManager.java:184)
    at ispfdesktop/desktop.core.database.CRUDTests.setUpBeforeClass(CRUDTests.java:21)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptLifecycleMethod(TimeoutExtension.java:126)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptBeforeAllMethod(TimeoutExtension.java:68)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.lambda$invokeBeforeAllMethods$9(ClassBasedTestDescriptor.java:384)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.invokeBeforeAllMethods(ClassBasedTestDescriptor.java:382)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.before(ClassBasedTestDescriptor.java:196)
    at org.junit.jupiter.engine.descriptor.ClassBasedTestDescriptor.before(ClassBasedTestDescriptor.java:78)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:136)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:84)
    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:98)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:40)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:529)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:756)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:452)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)
Caused by: java.io.FileNotFoundException: resource /desktop/core/database/databaseCreation.sql
    at com.h2database@2.1.210/org.h2.store.fs.disk.FilePathDisk.newInputStream(FilePathDisk.java:386)
    at com.h2database@2.1.210/org.h2.store.fs.FileUtils.newInputStream(FileUtils.java:267)
    at com.h2database@2.1.210/org.h2.command.dml.ScriptBase.openInput(ScriptBase.java:166)
    ... 69 more
Trying to access file using getResource (DatabaseManager class is in desktop.core.database package) tells that file exists:
String file = DatabaseManager.class.getResource("databaseCreation.sql").getFile();
boolean yes = new File(file).exists(); // yes is true
Tried on both Windows(10) and Linux (Kubuntu) platform and using h2 of version 2.1.210.
UPDATE #1
File is found when it is in root classpath folder classpath:databaseCreation.sql, but still not when under some subfolder like desktop/core/database.
Appending '/' before first subfolder does not work.
Tried to put sql file to all folders.
'classpath:desktop/core/database/databaseCreation.sql' does not work
'classpath:desktop/core/databaseCreation.sql' does not work
'classpath:desktop/databaseCreation.sql' does not work
only this works
'classpath:databaseCreation.sql'
Without using classpath:
Without using classpath, the file can be in any subfolders, but this way, i need to use absolute path to the file:
jdbc:h2:mem:;INIT=RUNSCRIPT FROM '<absolute path here>'
Leaving the question open since the referenced question has outdated answer, which is not working on current H2 version and want to know how to get it work using classpath.
UPDATE #2
In order to replicate, you need to use java modular system (module-info.java) in the project.

 
    