Revert "Googletest export": Remove test for empty prefix

This reverts commit 4c25e2b8.
Reason for revert: Reverting the commit that disallows empty prefixes.

Original commit message:

    Remove a test case rendered obsolete by disallowing empty argument for INSTANTIATE_TEST_SUITE_P.
    Remove the code that it was testing.

googletest/include/gtest/internal/gtest-param-util.h

@@ -574,7 +574,10 @@ class ParameterizedTestSuiteInfo : public ParameterizedTestSuiteInfoBase {
 
           test_param_names.insert(param_name);
 
-          test_name_stream << test_info->test_base_name << "/" << param_name;
+          if (!test_info->test_base_name.empty()) {
+            test_name_stream << test_info->test_base_name << "/";
+          }
+          test_name_stream << param_name;
           MakeAndRegisterTestInfo(
               test_suite_name.c_str(), test_name_stream.GetString().c_str(),
               nullptr,  // No type parameter.

googletest/test/googletest-output-test-golden-lin.txt

@@ -12,7 +12,7 @@ Expected equality of these values:
   3
 Stack trace: (omitted)
 
-[==========] Running 85 tests from 40 test suites.
+[==========] Running 86 tests from 41 test suites.
 [----------] Global test environment set-up.
 FooEnvironment::SetUp() called.
 BarEnvironment::SetUp() called.
@@ -966,6 +966,9 @@ Expected equality of these values:
 Stack trace: (omitted)
 
 [  FAILED  ] PrintingFailingParams/FailingParamTest.Fails/0, where GetParam() = 2
+[----------] 1 test from All/EmptyBasenameParamInst
+[ RUN      ] All/EmptyBasenameParamInst.Passes/0
+[       OK ] All/EmptyBasenameParamInst.Passes/0
 [----------] 2 tests from PrintingStrings/ParamTest
 [ RUN      ] PrintingStrings/ParamTest.Success/a
 [       OK ] PrintingStrings/ParamTest.Success/a
@@ -998,8 +1001,8 @@ Failed
 Expected fatal failure.
 Stack trace: (omitted)
 
-[==========] 85 tests from 40 test suites ran.
-[  PASSED  ] 31 tests.
+[==========] 86 tests from 41 test suites ran.
+[  PASSED  ] 32 tests.
 [  FAILED  ] 54 tests, listed below:
 [  FAILED  ] NonfatalFailureTest.EscapesStringOperands
 [  FAILED  ] NonfatalFailureTest.DiffForLongStrings

googletest/test/googletest-output-test_.cc

@@ -96,6 +96,14 @@ INSTANTIATE_TEST_SUITE_P(PrintingFailingParams,
                          FailingParamTest,
                          testing::Values(2));
 
+// Tests that an empty value for the test suite basename yields just
+// the test name without any prior /
+class EmptyBasenameParamInst : public testing::TestWithParam<int> {};
+
+TEST_P(EmptyBasenameParamInst, Passes) { EXPECT_EQ(1, GetParam()); }
+
+INSTANTIATE_TEST_SUITE_P(All, EmptyBasenameParamInst, testing::Values(1));
+
 static const char kGoldenString[] = "\"Line\0 1\"\nLine 2";
 
 TEST(NonfatalFailureTest, EscapesStringOperands) {