The Property That Wouldn’t Move
H2 in MODE=PostgreSQL has been the test database since the ledger’s inception. It emulates PostgreSQL syntax well enough for JPQL, but as native SQL crept in — LedgerSequenceAllocator uses a SQL-standard MERGE INTO for atomic per-subject sequence allocation — the gap between “tests pass” and “correct on PostgreSQL” widened. I wanted to add real PostgreSQL as an additive test layer without touching the existing H2 suite.
The design looked clean: a QuarkusTestResourceLifecycleManager starts a Testcontainers PostgreSQL container and returns the JDBC URL, username, password, and db-kind=postgresql. Test resource config has the highest ordinal in the Quarkus config system — it overrides everything. Test variants extend the existing H2 test classes, inheriting all test methods. Zero duplication.
Except quarkus.datasource.db-kind is a build-time property. It gets baked into the application during augmentation, before the test resource’s start() method ever runs. The highest config ordinal in the world doesn’t matter if the property was already consumed and discarded.
The error message is clear enough once it fires: “Build time property cannot be changed at runtime: quarkus.datasource.db-kind is set to ‘postgresql’ but it is build time fixed to ‘h2’.” But the path to triggering it is not obvious at all. Nothing in the QuarkusTestResourceLifecycleManager API signals that its config map has a class of properties it simply cannot influence. The ordinal model suggests a total ordering — it doesn’t advertise that build-time properties exist in a separate universe.
The fix is a clean split. db-kind=postgresql goes in PostgreSQLTestProfile.getConfigOverrides(), which participates in augmentation and triggers re-augmentation when the value differs from the default. Runtime properties — the JDBC URL, credentials — stay in the test resource where they belong. Build-time config in the profile; runtime config in the resource. Each property in the layer that can actually influence it.
A second surprise: the case-insensitive assertion. The parent test checked for a unique constraint violation by name — hasMessageContaining("IDX_LEDGER_ENTRY_SUBJECT_SEQ"). H2 uppercases all unquoted identifiers; PostgreSQL preserves lowercase. The fix was hasMessageMatching("(?is).*idx_ledger_entry_subject_seq.*") — the s flag (DOTALL) was necessary because H2 wraps its error messages across multiple lines, and without it . won’t match newlines. A one-line fix, but it took a test failure to surface.
The result is four new files: a test resource, an abstract profile base, and two test variants that inherit every test method from their H2 parents. The pattern extends trivially — any future test that needs real PostgreSQL adds a 17-line class extending its H2 counterpart.