SERVER-39000 Fix Unittest Framework initialization.

Some tests in `dbtest` do not use the `mongo::unittest::Test` class
as a basis for their implementation and thus need some way to benefit
from global DB Environment initialization functions.  Specifically
the changes in SERVER-32630 required `serverCompatibilityVersion`
to be set sensibly.  Some tests in `dbtest` were not correctly
getting this benefit; instead only incidentally getting a correct
setting by accident, as the results of an unintended residue of
an earlier operation.  This can lead to inconsistentcies in which
tests pass, as link order changes -- the tests are registered using
static initialization, whose instability of order can cause
mysterious failures in `dbtest`.

2 files changed, 46 insertions, 24 deletions

diff --git a/src/mongo/unittest/unittest.cpp b/src/mongo/unittest/unittest.cpp
index ac8c1947f7d..1eef67c81d7 100644
--- a/src/mongo/unittest/unittest.cpp
+++ b/src/mongo/unittest/unittest.cpp
@@ -1,4 +1,3 @@
-
 /**
  *    Copyright (C) 2018-present MongoDB, Inc.
  *
@@ -166,6 +165,38 @@ UnsafeScopeGuard<F> MakeUnsafeScopeGuard(F fun) {
     return UnsafeScopeGuard<F>(std::move(fun));
 }
 
+// Attempting to read the featureCompatibilityVersion parameter before it is explicitly initialized
+// with a meaningful value will trigger failures as of SERVER-32630.
+void setUpFCV() {
+    serverGlobalParams.featureCompatibility.setVersion(
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+}
+void tearDownFCV() {
+    serverGlobalParams.featureCompatibility.reset();
+}
+
+struct TestSuiteEnvironment {
+    explicit TestSuiteEnvironment() {
+        setUpFCV();
+    }
+
+    ~TestSuiteEnvironment() noexcept(false) {
+        tearDownFCV();
+    }
+};
+
+struct UnitTestEnvironment {
+    explicit UnitTestEnvironment(Test* const t) : test(t) {
+        test->setUp();
+    }
+
+    ~UnitTestEnvironment() noexcept(false) {
+        test->tearDown();
+    }
+
+    Test* const test;
+};
+
 }  // namespace
 
 Test::Test() : _isCapturingLogMessages(false) {}
@@ -177,8 +208,7 @@ Test::~Test() {
 }
 
 void Test::run() {
-    setUp();
-    auto guard = MakeUnsafeScopeGuard([this] { tearDown(); });
+    UnitTestEnvironment environment(this);
 
     // An uncaught exception does not prevent the tear down from running. But
     // such an event still constitutes an error. To test this behavior we use a
@@ -186,21 +216,11 @@ void Test::run() {
     // not considered an error.
     try {
         _doTest();
-    } catch (FixtureExceptionForTesting&) {
+    } catch (const FixtureExceptionForTesting&) {
         return;
     }
 }
 
-// Attempting to read the featureCompatibilityVersion parameter before it is explicitly initialized
-// with a meaningful value will trigger failures as of SERVER-32630.
-void Test::setUp() {
-    serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
-}
-void Test::tearDown() {
-    serverGlobalParams.featureCompatibility.reset();
-}
-
 namespace {
 class StringVectorAppender : public logger::MessageLogDomain::EventAppender {
 public:
@@ -309,7 +329,9 @@ Result* Suite::run(const std::string& filter, int runsPerTest) {
                 if (runsPerTest > 1) {
                     runTimes << "  (" << x + 1 << "/" << runsPerTest << ")";
                 }
+
                 log() << "\t going to run test: " << tc->getName() << runTimes.str();
+                TestSuiteEnvironment environment;
                 tc->run();
             }
             passes = true;
diff --git a/src/mongo/unittest/unittest.h b/src/mongo/unittest/unittest.h
index 1a6f82a9a36..4614b7a5abd 100644
--- a/src/mongo/unittest/unittest.h
+++ b/src/mongo/unittest/unittest.h
@@ -306,6 +306,16 @@ public:
 
     void run();
 
+    /**
+     * Called on the test object before running the test.
+     */
+    virtual void setUp() {}
+
+    /**
+     * Called on the test object after running the test.
+     */
+    virtual void tearDown() {}
+
 protected:
     /**
      * Registration agent for adding tests to suites, used by TEST macro.
@@ -363,16 +373,6 @@ protected:
      */
     void printCapturedLogLines() const;
 
-    /**
-     * Called on the test object before running the test.
-     */
-    virtual void setUp();
-
-    /**
-     * Called on the test object after running the test.
-     */
-    virtual void tearDown();
-
 private:
     /**
      * The test itself.