Add framework for executing tests against multiple postgresql versions using docker compose.

tests/pgintegration/PgTestEnvironment.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <gtest/gtest.h>
+#include <optional>
+#include <QString>
+
+namespace pgtest {
+
+/// Value of the TEST_DATABASE_URL environment variable, if set and non-empty.
+std::optional<QString> baseUrl();
+
+/// Same as baseUrl() but with the database name replaced.
+QString urlForDb(const QString &db);
+
+/// True when a server is configured and the template database was created.
+bool available();
+
+/// server_version_num of the server under test (0 when unavailable).
+int serverVersionNum();
+
+/// Portable process id.
+qint64 processId();
+
+/// Name of the template database for this process.
+QString templateDbName();
+
+/// Quotes an identifier for use in SQL.
+QString quoteIdent(const QString &name);
+
+/// Global environment, register it in main():
+///   ::testing::AddGlobalTestEnvironment(new pgtest::PgEnv(PGTEST_FIXTURE_DIR));
+/// Creates a template database from <fixtureDir>/schema.sql once per process.
+class PgEnv : public ::testing::Environment {
+public:
+    explicit PgEnv(QString fixtureDir) : fixtureDir_(std::move(fixtureDir)) {}
+    void SetUp() override;
+    void TearDown() override;
+
+private:
+    QString fixtureDir_;
+};
+
+} // namespace pgtest
+
+#define REQUIRE_PG_AT_LEAST(v) \
+    if (pgtest::serverVersionNum() < (v) * 10000) GTEST_SKIP() << "needs PG " #v