Set up postgresql testcontainers

- add .json to .editorconfig
- add spring-configuration-metadata.json
- update README.md
- add testcontainers dependencies
- add PostgresContainer
- add PostgresInitializer

src/main/kotlin/ltd/hlaeja/test/container/PostgresExtension.kt

@@ -0,0 +1,74 @@
+package ltd.hlaeja.test.container
+
+import java.io.BufferedReader
+import java.io.InputStreamReader
+import org.junit.jupiter.api.extension.AfterAllCallback
+import org.junit.jupiter.api.extension.BeforeAllCallback
+import org.junit.jupiter.api.extension.ExtensionContext
+import org.springframework.core.io.ClassPathResource
+import org.springframework.test.context.junit.jupiter.SpringExtension
+import kotlinx.coroutines.runBlocking
+import io.r2dbc.spi.Connection
+import io.r2dbc.spi.ConnectionFactory
+import kotlinx.coroutines.reactive.awaitFirstOrElse
+import kotlinx.coroutines.reactive.awaitFirstOrNull
+
+class PostgresExtension : BeforeAllCallback, AfterAllCallback {
+
+    override fun beforeAll(context: ExtensionContext) {
+        executeSqlFile(context, "postgres/data.sql")
+    }
+
+    override fun afterAll(context: ExtensionContext) {
+        executeSqlFile(context, "postgres/reset.sql")
+    }
+
+    private fun executeSqlFile(
+        context: ExtensionContext,
+        resourceSourcePath: String,
+    ) = runBlocking {
+        if (ClassPathResource(resourceSourcePath).exists()) {
+            executeSqlStatements(
+                postgresConnection(context),
+                makeSqlStatements(ClassPathResource(resourceSourcePath)),
+            )
+        }
+    }
+
+    @Suppress("TooGenericExceptionThrown")
+    private suspend fun postgresConnection(
+        context: ExtensionContext,
+    ) = SpringExtension.getApplicationContext(context)
+        .getBean(ConnectionFactory::class.java)
+        .create()
+        .awaitFirstOrElse { throw RuntimeException("Connection factory could not be created") }
+
+    private suspend fun executeSqlStatements(
+        connection: Connection,
+        statements: List<String>,
+    ) {
+        try {
+            statements.forEach { statement ->
+                connection.createStatement(statement)
+                    .execute()
+                    .awaitFirstOrNull()
+            }
+        } finally {
+            connection.close().awaitFirstOrNull()
+        }
+    }
+
+    private fun makeSqlStatements(
+        classPathResource: ClassPathResource,
+    ): List<String> = classPathResource.inputStream.use { inputStream ->
+        BufferedReader(InputStreamReader(inputStream))
+            .lines()
+            .filter { it.isNotEmpty() && !it.startsWith("--") }
+            .map { it.trim() }
+            .toList()
+            .joinToString(" ")
+            .split(';')
+            .filter { it.isNotBlank() }
+            .map { "${it.trim()};" }
+    }
+}