diff --git a/flang/unittests/CMakeLists.txt b/flang/unittests/CMakeLists.txt
--- a/flang/unittests/CMakeLists.txt
+++ b/flang/unittests/CMakeLists.txt
@@ -40,6 +40,7 @@
 add_subdirectory(Decimal)
 add_subdirectory(Evaluate)
 add_subdirectory(Runtime)
+add_subdirectory(RuntimeGTest)
 
 if (FLANG_BUILD_NEW_DRIVER)
   add_subdirectory(Frontend)
diff --git a/flang/unittests/RuntimeGTest/CMakeLists.txt b/flang/unittests/RuntimeGTest/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/flang/unittests/RuntimeGTest/CMakeLists.txt
@@ -0,0 +1,9 @@
+add_flang_unittest(FlangRuntimeTests
+  CharacterTest.cpp
+  RuntimeTesting.cpp
+)
+
+target_link_libraries(FlangRuntimeTests
+  PRIVATE
+  FortranRuntime
+)
diff --git a/flang/unittests/RuntimeGTest/CharacterTest.cpp b/flang/unittests/RuntimeGTest/CharacterTest.cpp
new file mode 100644
--- /dev/null
+++ b/flang/unittests/RuntimeGTest/CharacterTest.cpp
@@ -0,0 +1,74 @@
+// Basic sanity tests of CHARACTER API; exhaustive testing will be done
+// in Fortran.
+
+#include "../../runtime/character.h"
+#include "RuntimeTesting.h"
+#include "gtest/gtest.h"
+#include <array>
+#include <cstring>
+#include <tuple>
+
+using namespace Fortran::runtime;
+
+struct CharacterTests : RuntimeTestFixture {};
+
+TEST_F(CharacterTests, AppendAndPad) {
+  for (std::size_t limit{0}; limit < 8; ++limit) {
+    char x[8];
+    std::size_t xLen{0};
+    std::memset(x, 0, sizeof x);
+    xLen = RTNAME(CharacterAppend1)(x, limit, xLen, "abc", 3);
+    xLen = RTNAME(CharacterAppend1)(x, limit, xLen, "DE", 2);
+    RTNAME(CharacterPad1)(x, limit, xLen);
+    ASSERT_LE(xLen, limit) << "xLen " << xLen << ">" << limit;
+    if (x[limit]) {
+      EXPECT_TRUE(false) << "x[" << limit << "]='" << x[limit] << "'\n";
+      x[limit] = '\0';
+    }
+    ASSERT_FALSE(std::memcmp(x, "abcDE   ", limit)) << "x = '" << x << "'";
+  }
+}
+
+using ParamT = std::tuple<const char *, const char *, int, int, int>;
+
+struct CharacterComparisonTestsFixture
+    : public RuntimeTestFixture,
+      public ::testing::WithParamInterface<ParamT> {
+  void SetUp() {
+    RuntimeTestFixture::SetUp();
+    std::tie(x, y, xBytes, yBytes, expect) = GetParam();
+  }
+  void SwapParams() {
+    std::swap(x, y);
+    std::swap(xBytes, yBytes);
+    expect = -expect;
+  }
+  void DoCharacterComparison() {
+    int cmp{RTNAME(CharacterCompareScalar1)(x, y, xBytes, yBytes)};
+    char buf[2][8];
+    std::memset(buf, 0, sizeof buf);
+    std::memcpy(buf[0], x, xBytes);
+    std::memcpy(buf[1], y, yBytes);
+    ASSERT_EQ(cmp, expect) << "compare '" << buf[0] << "'(" << xBytes
+                           << ") to '" << buf[1] << "'(" << yBytes << "), got "
+                           << cmp << ", should be " << expect << '\n';
+  }
+  const char *x;
+  const char *y;
+  int xBytes;
+  int yBytes;
+  int expect;
+};
+
+TEST_P(CharacterComparisonTestsFixture, CompareCharacters) {
+  DoCharacterComparison();
+  SwapParams();
+  DoCharacterComparison();
+}
+
+INSTANTIATE_TEST_CASE_P(CharacterComparisonTests,
+    CharacterComparisonTestsFixture,
+    ::testing::Values(std::make_tuple("abc", "abc", 3, 3, 0),
+        std::make_tuple("abc", "def", 3, 3, -1),
+        std::make_tuple("ab ", "abc", 3, 2, 0),
+        std::make_tuple("abc", "abc", 2, 3, -1)), );
diff --git a/flang/unittests/RuntimeGTest/RuntimeTesting.h b/flang/unittests/RuntimeGTest/RuntimeTesting.h
new file mode 100644
--- /dev/null
+++ b/flang/unittests/RuntimeGTest/RuntimeTesting.h
@@ -0,0 +1,19 @@
+#ifndef LLVM_FLANG_UNITTESTS_RUNTIMEGTEST_RUNTIMETESTING_H
+#define LLVM_FLANG_UNITTESTS_RUNTIMEGTEST_RUNTIMETESTING_H
+
+#include "gtest/gtest.h"
+#include <cstddef>
+
+struct RuntimeTestFixture : ::testing::Test {
+  RuntimeTestFixture();
+  void SetUp();
+  void TearDown();
+
+private:
+  bool IsCrashHandlerRegistered;
+};
+
+// Defines a CHARACTER object with padding when needed
+void SetCharacter(char *, std::size_t, const char *);
+
+#endif // LLVM_FLANG_UNITTESTS_RUNTIMEGTEST_RUNTIMETESTING_H
diff --git a/flang/unittests/RuntimeGTest/RuntimeTesting.cpp b/flang/unittests/RuntimeGTest/RuntimeTesting.cpp
new file mode 100644
--- /dev/null
+++ b/flang/unittests/RuntimeGTest/RuntimeTesting.cpp
@@ -0,0 +1,43 @@
+#include "RuntimeTesting.h"
+#include "../../runtime/terminator.h"
+#include <algorithm>
+#include <cstdarg>
+#include <cstdio>
+#include <cstring>
+#include <string>
+
+static int failures{0};
+
+// Override the Fortran runtime's Crash() for testing purposes
+static void CatchCrash(
+    const char *sourceFile, int sourceLine, const char *message, va_list &ap) {
+  char buffer[1000];
+  std::vsnprintf(buffer, sizeof buffer, message, ap);
+  va_end(ap);
+  llvm::errs() << (sourceFile ? sourceFile : "unknown source file") << '('
+               << sourceLine << "): CRASH: " << buffer << '\n';
+  failures++;
+}
+
+RuntimeTestFixture::RuntimeTestFixture() : IsCrashHandlerRegistered{false} {}
+
+void RuntimeTestFixture::SetUp() {
+  if (not IsCrashHandlerRegistered)
+    Fortran::runtime::Terminator::RegisterCrashHandler(CatchCrash);
+  IsCrashHandlerRegistered = true;
+}
+
+void RuntimeTestFixture::TearDown() {
+  ASSERT_EQ(failures, 0)
+      << "Found " << failures << " runtime crashes in teardown phase of test "
+      << ::testing::UnitTest::GetInstance()->current_test_info()->name();
+  failures = 0;
+}
+
+void SetCharacter(char *to, std::size_t n, const char *from) {
+  auto len{std::strlen(from)};
+  std::memcpy(to, from, std::min(len, n));
+  if (len < n) {
+    std::memset(to + len, ' ', n - len);
+  }
+}