Add ShellStrategy

`ShellStrategy` can also be used as `Wait.forSuccessfulCommand(...)`.

Co-authored-by: Eddú Meléndez <eddu.melendez@gmail.com>

core/src/main/java/org/testcontainers/containers/wait/strategy/ShellStrategy.java

@@ -0,0 +1,32 @@
+package org.testcontainers.containers.wait.strategy;
+
+import org.rnorth.ducttape.TimeoutException;
+import org.rnorth.ducttape.unreliables.Unreliables;
+import org.testcontainers.containers.ContainerLaunchException;
+
+import java.util.concurrent.TimeUnit;
+
+public class ShellStrategy extends AbstractWaitStrategy {
+
+    private String command;
+
+    public ShellStrategy withCommand(String command) {
+        this.command = command;
+        return this;
+    }
+
+    @Override
+    protected void waitUntilReady() {
+        try {
+            Unreliables.retryUntilTrue(
+                (int) startupTimeout.getSeconds(),
+                TimeUnit.SECONDS,
+                () -> waitStrategyTarget.execInContainer("/bin/sh", "-c", this.command).getExitCode() == 0
+            );
+        } catch (TimeoutException e) {
+            throw new ContainerLaunchException(
+                "Timed out waiting for container to execute `" + this.command + "` successfully."
+            );
+        }
+    }
+}

core/src/main/java/org/testcontainers/containers/wait/strategy/Wait.java

@@ -66,4 +66,14 @@ public static LogMessageWaitStrategy forLogMessage(String regex, int times) {
     public static DockerHealthcheckWaitStrategy forHealthcheck() {
         return new DockerHealthcheckWaitStrategy();
     }
+
+    /**
+     * Convenience method to return a WaitStrategy for a shell command.
+     *
+     * @param command the command to run
+     * @return ShellStrategy
+     */
+    public static ShellStrategy forSuccessfulCommand(String command) {
+        return new ShellStrategy().withCommand(command);
+    }
 }

core/src/test/java/org/testcontainers/junit/wait/strategy/ShellStrategyTest.java

@@ -0,0 +1,42 @@
+package org.testcontainers.junit.wait.strategy;
+
+import org.jetbrains.annotations.NotNull;
+import org.junit.Test;
+import org.testcontainers.containers.wait.strategy.ShellStrategy;
+
+import java.util.concurrent.atomic.AtomicBoolean;
+
+/**
+ * Tests for {@link ShellStrategy}.
+ */
+public class ShellStrategyTest extends AbstractWaitStrategyTest<ShellStrategy> {
+
+    private static final String LOCK_FILE = "/tmp/ready.lock";
+
+    @Test
+    public void testWaitUntilReady_Success() {
+        waitUntilReadyAndSucceed(String.format("touch %s; sleep 300", LOCK_FILE));
+    }
+
+    @Test
+    public void testWaitUntilReady_Timeout() {
+        waitUntilReadyAndTimeout("sleep 300");
+    }
+
+    @NotNull
+    @Override
+    protected ShellStrategy buildWaitStrategy(AtomicBoolean ready) {
+        return createShellStrategy(ready).withCommand(String.format("stat %s", LOCK_FILE));
+    }
+
+    @NotNull
+    private static ShellStrategy createShellStrategy(AtomicBoolean ready) {
+        return new ShellStrategy() {
+            @Override
+            protected void waitUntilReady() {
+                super.waitUntilReady();
+                ready.set(true);
+            }
+        };
+    }
+}