test(transactions): ensure test runner properly excludes sharded

Test runner was attempting to run sharded transaction tests
against 4.0.x servers. Modified the way tests are created
so that different topologies have different version requirements

Fixes NODE-1890

Author: daprahamian

test/functional/transactions_tests.js

@@ -239,39 +239,42 @@ function generateTopologyTests(testSuites, testContext) {
   testSuites.forEach(testSuite => {
     const suiteName = testSuite.name;
     const topologies = parseTopologies(testSuite.topology);
-    const minServerVersion = testSuite.minServerVersion
-      ? `>=${testSuite.minServerVersion}`
-      : '>=3.7.x';
 
     const tests = testSuite.tests;
-    describe(suiteName, {
-      metadata: { requires: { topology: topologies, mongodb: minServerVersion } },
-      test: function() {
-        beforeEach(() => prepareDatabaseForSuite(testSuite, testContext));
-        afterEach(() => testContext.cleanupAfterSuite());
-
-        tests.forEach(spec => {
-          const maybeSkipIt = shouldSkipTest(spec);
-          maybeSkipIt(spec.description, function() {
-            let testPromise = Promise.resolve();
-
-            if (spec.failPoint) {
-              testPromise = testPromise.then(() => testContext.enableFailPoint(spec.failPoint));
-            }
-
-            // run the actual test
-            testPromise = testPromise.then(() =>
-              runTestSuiteTest(this.configuration, spec, testContext)
-            );
-
-            if (spec.failPoint) {
-              testPromise = testPromise.then(() => testContext.disableFailPoint(spec.failPoint));
-            }
-
-            return testPromise.then(() => validateOutcome(spec, testContext));
+    topologies.forEach(topology => {
+      const DEFAULT_MIN_SERVER_VERSION = topology === 'sharded' ? '>=4.1.5' : '>=3.7.x';
+      const minServerVersion = testSuite.minServerVersion
+        ? `>=${testSuite.minServerVersion}`
+        : DEFAULT_MIN_SERVER_VERSION;
+      describe(`${suiteName} - ${topology}`, {
+        metadata: { requires: { topology: [topology], mongodb: minServerVersion } },
+        test: function() {
+          beforeEach(() => prepareDatabaseForSuite(testSuite, testContext));
+          afterEach(() => testContext.cleanupAfterSuite());
+
+          tests.forEach(spec => {
+            const maybeSkipIt = shouldSkipTest(spec);
+            maybeSkipIt(spec.description, function() {
+              let testPromise = Promise.resolve();
+
+              if (spec.failPoint) {
+                testPromise = testPromise.then(() => testContext.enableFailPoint(spec.failPoint));
+              }
+
+              // run the actual test
+              testPromise = testPromise.then(() =>
+                runTestSuiteTest(this.configuration, spec, testContext)
+              );
+
+              if (spec.failPoint) {
+                testPromise = testPromise.then(() => testContext.disableFailPoint(spec.failPoint));
+              }
+
+              return testPromise.then(() => validateOutcome(spec, testContext));
+            });
           });
-        });
-      }
+        }
+      });
     });
   });
 }