Add base shell test system

- NOTE: very much wip and unstable
- This commit is a first step to provide boot style
  @ShellTest annotation
- New modules spring-shell-test and spring-shell-test-autoconfigure
- Focus is to autoconfigure context without shell runners so that
  we can create "sessions" and hook to configures jline terminal
  with custom in/out streams.
- Skeleton fork from jediterm to provide basic terminal emulation
  to part of a control amd escape characters working.
- ShellTestClient is a concept user can use to interact with a shell
  in a same way user would use a "real" shell.
- Fixes #489

spring-shell-docs/src/main/asciidoc/using-shell-testing-basics.adoc

@@ -0,0 +1,25 @@
+[[using-shell-testing-basics]]
+==== Basics
+ifndef::snippets[:snippets: ../../test/java/org/springframework/shell/docs]
+
+Spring Shell provides a number of utilities and annotations to help when testing your application.
+Test support is provided by two modules: `spring-shell-test` contains core items, and
+`spring-shell-test-autoconfigure` supports auto-configuration for tests.
+
+To test _interactive_ commands.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/TestingSnippets.java[tag=testing-shelltest-interactive]
+----
+====
+
+To test _non-interactive_ commands.
+
+====
+[source, java, indent=0]
+----
+include::{snippets}/TestingSnippets.java[tag=testing-shelltest-noninteractive]
+----
+====

spring-shell-docs/src/main/asciidoc/using-shell-testing.adoc

@@ -0,0 +1,18 @@
+[[using-shell-testing]]
+== Testing
+ifndef::snippets[:snippets: ../../test/java/org/springframework/shell/docs]
+
+Testing cli application is difficult due to various reasons:
+
+- There are differences between OS's.
+- Within OS there may be different shell implementations in use.
+- What goes into a shell and comes out from a shell my be totally
+  different what you see in shell itself due to control characters.
+- Shell may feel syncronous but most likely it is not meaning when
+  someting is written into it, you can't assume next update in
+  in it is not final.
+
+NOTE: Testing support is currently under development and will be
+      unstable for various parts.
+
+include::using-shell-testing-basics.adoc[]

spring-shell-docs/src/main/asciidoc/using-shell.adoc

@@ -13,3 +13,5 @@ include::using-shell-components.adoc[]
 include::using-shell-customization.adoc[]
 
 include::using-shell-execution.adoc[]
+
+include::using-shell-testing.adoc[]

spring-shell-docs/src/test/java/org/springframework/shell/docs/TestingSnippets.java

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.docs;
+
+import java.util.concurrent.TimeUnit;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.shell.test.ShellAssertions;
+import org.springframework.shell.test.ShellTestClient;
+import org.springframework.shell.test.ShellTestClient.InteractiveShellSession;
+import org.springframework.shell.test.ShellTestClient.NonInteractiveShellSession;
+import org.springframework.shell.test.autoconfigure.ShellTest;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.annotation.DirtiesContext.ClassMode;
+
+import static org.awaitility.Awaitility.await;
+
+class TestingSnippets {
+
+	// tag::testing-shelltest-interactive[]
+	@ShellTest
+	@DirtiesContext(classMode = ClassMode.AFTER_EACH_TEST_METHOD)
+	class InteractiveTestSample {
+
+		@Autowired
+		ShellTestClient client;
+
+		@Test
+		void test() {
+			InteractiveShellSession session = client
+					.interactive()
+					.run();
+
+			await().atMost(2, TimeUnit.SECONDS).untilAsserted(() -> {
+				ShellAssertions.assertThat(session.screen())
+					.containsText("shell");
+			});
+
+			session.write(session.writeSequence().text("help").carriageReturn().build());
+			await().atMost(2, TimeUnit.SECONDS).untilAsserted(() -> {
+				ShellAssertions.assertThat(session.screen())
+					.containsText("AVAILABLE COMMANDS");
+			});
+		}
+	}
+	// end::testing-shelltest-interactive[]
+
+	// tag::testing-shelltest-noninteractive[]
+	@ShellTest
+	@DirtiesContext(classMode = ClassMode.AFTER_EACH_TEST_METHOD)
+	class NonInteractiveTestSample {
+
+		@Autowired
+		ShellTestClient client;
+
+		@Test
+		void test() {
+			NonInteractiveShellSession session = client
+				.nonInterative("help", "help")
+				.run();
+
+			await().atMost(2, TimeUnit.SECONDS).untilAsserted(() -> {
+				ShellAssertions.assertThat(session.screen())
+					.containsText("AVAILABLE COMMANDS");
+			});
+		}
+	}
+	// end::testing-shelltest-noninteractive[]
+}