Refactor `backend.js` #3 - legibility (#24084)

* Define all Java flags separately for readability

* Separate database and snowplow configs

* Explicitly say that we are generating a temporary DB file

* Extract `userDefaults` and warn about it

* Rename `databaseConfig` to `metabaseConfig`

* Rename temporary database path generator

frontend/test/__runner__/backend.js

@@ -8,7 +8,7 @@ const { spawn } = require("child_process");
 const fetch = require("isomorphic-fetch");
 
 let testDbId = 0;
-const getDbFile = () =>
+const generateTempDbPath = () =>
   path.join(os.tmpdir(), `metabase-test-${process.pid}-${testDbId++}.db`);
 
 let port = 4000;
@@ -16,7 +16,7 @@ const getPort = () => port++;
 
 const BackendResource = createSharedResource("BackendResource", {
   create({ dbKey }) {
-    const dbFile = getDbFile();
+    const dbFile = generateTempDbPath();
     const absoluteDbKey = dbKey ? __dirname + dbKey : dbFile;
     const e2eHost = process.env["E2E_HOST"];
     if (e2eHost) {
@@ -41,39 +41,58 @@ const BackendResource = createSharedResource("BackendResource", {
         fs.copyFileSync(`${server.dbKey}.mv.db`, `${server.dbFile}.mv.db`);
       }
 
+      const javaFlags = [
+        "-XX:+IgnoreUnrecognizedVMOptions", // ignore options not recognized by this Java version (e.g. Java 8 should ignore Java 9 options)
+        "-Dh2.bindAddress=localhost", // fix H2 randomly not working (?)
+        "-Djava.awt.headless=true", // when running on macOS prevent little Java icon from popping up in Dock
+        "-Duser.timezone=US/Pacific",
+        `-Dlog4j.configurationFile=file:${__dirname}/log4j2.xml`,
+      ];
+
+      const metabaseConfig = {
+        MB_DB_TYPE: "h2",
+        MB_DB_FILE: server.dbFile,
+        MB_JETTY_HOST: "0.0.0.0",
+        MB_JETTY_PORT: server.port,
+        MB_ENABLE_TEST_ENDPOINTS: "true",
+        MB_PREMIUM_EMBEDDING_TOKEN:
+          (process.env["MB_EDITION"] === "ee" &&
+            process.env["ENTERPRISE_TOKEN"]) ||
+          undefined,
+      };
+
+      /**
+       * This ENV is used for Cloud instances only, and is subject to change.
+       * As such, it is not documented anywhere in the code base!
+       *
+       * WARNING:
+       * Changing values here will break the related E2E test.
+       */
+      const userDefaults = {
+        MB_USER_DEFAULTS: JSON.stringify({
+          token: "123456",
+          user: {
+            first_name: "Testy",
+            last_name: "McTestface",
+            email: "testy@metabase.test",
+            site_name: "Epic Team",
+          },
+        }),
+      };
+
+      const snowplowConfig = {
+        MB_SNOWPLOW_AVAILABLE: process.env["MB_SNOWPLOW_AVAILABLE"],
+        MB_SNOWPLOW_URL: process.env["MB_SNOWPLOW_URL"],
+      };
+
       server.process = spawn(
         "java",
-        [
-          "-XX:+IgnoreUnrecognizedVMOptions", // ignore options not recognized by this Java version (e.g. Java 8 should ignore Java 9 options)
-          "-Dh2.bindAddress=localhost", // fix H2 randomly not working (?)
-          "-Djava.awt.headless=true", // when running on macOS prevent little Java icon from popping up in Dock
-          "-Duser.timezone=US/Pacific",
-          `-Dlog4j.configurationFile=file:${__dirname}/log4j2.xml`,
-          "-jar",
-          "target/uberjar/metabase.jar",
-        ],
+        [...javaFlags, "-jar", "target/uberjar/metabase.jar"],
         {
           env: {
-            MB_DB_TYPE: "h2",
-            MB_DB_FILE: server.dbFile,
-            MB_JETTY_HOST: "0.0.0.0",
-            MB_JETTY_PORT: server.port,
-            MB_ENABLE_TEST_ENDPOINTS: "true",
-            MB_PREMIUM_EMBEDDING_TOKEN:
-              (process.env["MB_EDITION"] === "ee" &&
-                process.env["ENTERPRISE_TOKEN"]) ||
-              undefined,
-            MB_USER_DEFAULTS: JSON.stringify({
-              token: "123456",
-              user: {
-                first_name: "Testy",
-                last_name: "McTestface",
-                email: "testy@metabase.test",
-                site_name: "Epic Team",
-              },
-            }),
-            MB_SNOWPLOW_AVAILABLE: process.env["MB_SNOWPLOW_AVAILABLE"],
-            MB_SNOWPLOW_URL: process.env["MB_SNOWPLOW_URL"],
+            ...metabaseConfig,
+            ...userDefaults,
+            ...snowplowConfig,
             PATH: process.env.PATH,
           },
           stdio:

frontend/test/metabase/scenarios/onboarding/setup/setup.cy.spec.js

@@ -211,6 +211,7 @@ describe("scenarios > setup", () => {
     cy.location("pathname").should("eq", "/");
   });
 
+  // Values in this test are set through MB_USER_DEFAULTS environment variable!
   // Please see https://github.com/metabase/metabase/pull/18763 for details
   it("should allow pre-filling user details", () => {
     cy.visit(`/setup#123456`);