feat(backend): update DB layer with tests

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/db/db.go

@@ -16,7 +16,7 @@ var DB *pgxpool.Pool
 func Connect() error {
 	// Connect to Postgres on local network (127.x.x.x)
 	dsn := fmt.Sprintf(
-		"postgres://%s:%s@%s:5432/%s",
+		"postgres://%s:%s@%s:5432/%s?require_auth=scram-sha-256",
 		getEnv("POSTGRES_USER"),
 		getEnv("POSTGRES_PASSWORD"),
 		getEnv("POSTGRES_HOST"),

backend/db/db_dev.go

@@ -16,7 +16,7 @@ var DB *pgxpool.Pool
 func Connect() error {
 	// Connect to Postgres inside Docker network
 	dsn := fmt.Sprintf(
-		"postgres://%s:%s@localhost:5432/%s?sslmode=disable",
+		"postgres://%s:%s@localhost:5432/%s?sslmode=disable&require_auth=scram-sha-256",
 		getEnv("POSTGRES_USER"),
 		getEnv("POSTGRES_PASSWORD"),
 		getEnv("POSTGRES_DB"),

backend/db/db_test.go

@@ -0,0 +1,185 @@
+//go:build test
+// +build test
+
+package db
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"sync"
+	"testing"
+)
+
+func resetEnv() {
+	os.Setenv("POSTGRES_USER", "myuser")
+	os.Setenv("POSTGRES_PASSWORD", "mypassword")
+	os.Setenv("POSTGRES_HOST", "localhost")
+	os.Setenv("POSTGRES_DB", "crussell_test")
+}
+
+func closePool() {
+	if DB != nil {
+		DB.Close()
+		DB = nil
+	}
+}
+
+// =============================================================================
+// Happy path — connect + ping
+// =============================================================================
+
+func TestConnect_Success(t *testing.T) {
+	closePool()
+	resetEnv()
+
+	err := Connect()
+	if err != nil {
+		t.Fatalf("Connect() failed: %v", err)
+	}
+	defer closePool()
+
+	if DB == nil {
+		t.Fatal("DB is nil after successful Connect")
+	}
+}
+
+func TestConnect_PingViaTestDB(t *testing.T) {
+	closePool()
+	resetEnv()
+
+	err := Connect()
+	if err != nil {
+		t.Fatalf("Connect() failed: %v", err)
+	}
+	defer closePool()
+
+	conn, err := DB.Acquire(context.Background())
+	if err != nil {
+		t.Fatalf("Acquire failed: %v", err)
+	}
+	defer conn.Release()
+
+	var result int
+	err = conn.QueryRow(context.Background(), "SELECT 1").Scan(&result)
+	if err != nil {
+		t.Fatalf("Ping query failed: %v", err)
+	}
+	if result != 1 {
+		t.Errorf("expected 1, got %d", result)
+	}
+}
+
+// =============================================================================
+// Connection failure scenarios
+// =============================================================================
+
+func TestConnect_InvalidCredentials(t *testing.T) {
+	closePool()
+
+	os.Setenv("POSTGRES_USER", "wronguser")
+	os.Setenv("POSTGRES_PASSWORD", "wrongpassword")
+	os.Setenv("POSTGRES_DB", "crussell_test")
+	os.Setenv("POSTGRES_HOST", "localhost")
+
+	err := Connect()
+	if err == nil {
+		t.Error("expected error for invalid credentials, got nil")
+		closePool()
+	}
+
+	resetEnv()
+}
+
+func TestConnect_RefusedConnection(t *testing.T) {
+	closePool()
+
+	os.Setenv("POSTGRES_USER", "myuser")
+	os.Setenv("POSTGRES_PASSWORD", "mypassword")
+	os.Setenv("POSTGRES_DB", "crussell_test")
+	os.Setenv("POSTGRES_HOST", "localhost")
+
+	t.Skip("pgxpool.New is lazy — connection errors surface on Acquire, not Connect")
+
+	resetEnv()
+}
+
+// =============================================================================
+// Concurrent access — pool should handle parallel queries
+// =============================================================================
+
+func TestConcurrentQueries(t *testing.T) {
+	closePool()
+	resetEnv()
+
+	err := Connect()
+	if err != nil {
+		t.Fatalf("Connect() failed: %v", err)
+	}
+	defer closePool()
+
+	var wg sync.WaitGroup
+	errs := make(chan error, 20)
+
+	for i := 0; i < 20; i++ {
+		wg.Add(1)
+		go func(id int) {
+			defer wg.Done()
+			conn, err := DB.Acquire(context.Background())
+			if err != nil {
+				errs <- fmt.Errorf("goroutine %d: acquire: %w", id, err)
+				return
+			}
+			defer conn.Release()
+
+			var result int
+			err = conn.QueryRow(context.Background(), "SELECT $1::int", id).Scan(&result)
+			if err != nil {
+				errs <- fmt.Errorf("goroutine %d: query: %w", id, err)
+				return
+			}
+			if result != id {
+				errs <- fmt.Errorf("goroutine %d: expected %d, got %d", id, id, result)
+			}
+		}(i)
+	}
+
+	wg.Wait()
+	close(errs)
+
+	for e := range errs {
+		t.Error(e)
+	}
+}
+
+// =============================================================================
+// getEnv unit tests
+// =============================================================================
+
+func TestGetEnv_ReturnsValue(t *testing.T) {
+	os.Setenv("TEST_DB_VAR", "expected_value")
+	defer os.Unsetenv("TEST_DB_VAR")
+
+	if v := getEnv("TEST_DB_VAR"); v != "expected_value" {
+		t.Errorf("expected 'expected_value', got %q", v)
+	}
+}
+
+func TestGetEnv_ReturnsEmptyWhenUnset(t *testing.T) {
+	os.Unsetenv("TEST_DB_MISSING_VAR")
+
+	if v := getEnv("TEST_DB_MISSING_VAR"); v != "" {
+		t.Errorf("expected empty string, got %q", v)
+	}
+}
+
+// =============================================================================
+// Clean-up — restore env after all tests
+// =============================================================================
+
+func TestMain(m *testing.M) {
+	resetEnv()
+	code := m.Run()
+	closePool()
+	os.Exit(code)
+}