add initial unit test for {fmt} testing only conversions frequently used by LAMMPS

unittest/utils/CMakeLists.txt

@@ -5,3 +5,7 @@ add_test(Tokenizer test_tokenizer)
 add_executable(test_utils test_utils.cpp)
 target_link_libraries(test_utils PRIVATE lammps GTest::GMockMain GTest::GMock GTest::GTest)
 add_test(Utils test_utils)
+
+add_executable(test_fmtlib test_fmtlib.cpp)
+target_link_libraries(test_fmtlib PRIVATE lammps GTest::GMockMain GTest::GMock GTest::GTest)
+add_test(FmtLib test_fmtlib)

unittest/utils/test_fmtlib.cpp

@@ -0,0 +1,40 @@
+#include "lmptype.h"
+#include "gtest/gtest.h"
+#include "gmock/gmock.h"
+#include "fmt/format.h"
+#include <string>
+
+using namespace LAMMPS_NS;
+using ::testing::Eq;
+
+// this tests a subset of {fmt} that is most relevant to LAMMPS
+
+TEST(Fmtlib, insert_string) {
+    const char word[] = "word";
+    auto text = fmt::format("word {}",word);
+    ASSERT_THAT(text, Eq("word word"));
+}
+
+TEST(Fmtlib, insert_int) {
+    const int word = 333;
+    auto text = fmt::format("word {}",word);
+    ASSERT_THAT(text, Eq("word 333"));
+}
+
+TEST(Fmtlib, insert_neg_int) {
+    const int word = -333;
+    auto text = fmt::format("word {}",word);
+    ASSERT_THAT(text, Eq("word -333"));
+}
+
+TEST(Fmtlib, insert_double) {
+    const double word = 1.5;
+    auto text = fmt::format("word {}",word);
+    ASSERT_THAT(text, Eq("word 1.5"));
+}
+
+TEST(Fmtlib, insert_neg_double) {
+    const double word = -1.5;
+    auto text = fmt::format("word {}",word);
+    ASSERT_THAT(text, Eq("word 1.5"));
+}