Fix get version error when schemaversion table does not exist (#142)

lib/Client.js

@@ -71,6 +71,13 @@ class Client {
     return config.execQuery(query);
   }
 
+  async hasVersionTable() {
+    const sql = this.getColumnsSql();
+    const results = await this.runQuery(sql);
+    const { rows } = results;
+    return rows.length > 0;
+  }
+
   async ensureTable() {
     const { config } = this;
     const sql = this.getColumnsSql();

postgrator.js

@@ -112,6 +112,12 @@ class Postgrator extends EventEmitter {
    */
   async getDatabaseVersion() {
     const versionSql = this.commonClient.getDatabaseVersionSql();
+
+    const initialized = await this.commonClient.hasVersionTable();
+    if (!initialized) {
+      return undefined;
+    }
+
     const result = await this.commonClient.runQuery(versionSql);
     const version = result.rows.length > 0 ? result.rows[0].version : 0;
     return parseInt(version);

test/drivers.js

@@ -83,6 +83,11 @@ function driverExecQuery(factoryFunction, label) {
       await end();
     });
 
+    it("Returns undefined for database version before init", async function () {
+      const result = await postgrator.getDatabaseVersion();
+      assert.strictEqual(result, undefined);
+    });
+
     it("Migrates multiple versions up (000 -> 002)", function () {
       return postgrator
         .migrate("002")