add tests for lammps_eval() and its python counterpart

src/library.cpp

@@ -516,6 +516,9 @@ treated as part of the command and will **not** start a second command.
 The function returns the expanded string in a new string buffer that
 must be freed with :cpp:func:`lammps_free` after use to avoid a memory leak.
 
+*See also*
+    :cpp:func:`lammps_eval'
+
 \endverbatim
  *
  * \param  handle  pointer to a previously created LAMMPS instance
@@ -2910,10 +2913,13 @@ int lammps_variable_info(void *handle, int idx, char *buffer, int buf_size) {
 
 .. versionadded:: TBD
 
-This function takes a string with an expression, like what can be used
+This function takes a string with an expression that can be used
 for :doc:`equal style variables <variable>`, evaluates it and returns
 the resulting (scalar) value as a floating point number.
 
+*See also*
+    :cpp:func:`lammps_expand'
+
 \endverbatim
 
  * \param handle   pointer to a previously created LAMMPS instance cast to ``void *``.

unittest/c-library/test_library_objects.cpp

@@ -233,3 +233,34 @@ TEST_F(LibraryObjects, expand)
     EXPECT_THAT((char *)ptr, StrEq("'xx_$(4+5)_$(PI) ${one}-${two}-${three}'"));
     lammps_free(ptr);
 }
+
+TEST_F(LibraryObjects, eval)
+{
+    lammps_get_last_error_message(lmp, nullptr, 1);
+    ::testing::internal::CaptureStdout();
+    lammps_commands_string(lmp, "region box1 block 0 10 0 5 -0.5 0.5\n"
+                                "lattice fcc 0.8\n"
+                                "create_box 1 box1\n"
+                                "create_atoms 1 box\n"
+                                "mass * 1.0\n"
+                                "pair_style lj/cut 4.0\n"
+                                "pair_coeff * * 1.0 1.0\n"
+                                "variable t equal 15.0\n"
+                                "velocity all create 1.5 532656\n"
+                                "fix 1 all nve\n"
+                                "run 0 post no\n");
+    lammps_command(lmp, "variable one    index     1 2 3 4");
+    lammps_command(lmp, "variable two    equal     2");
+    std::string output = ::testing::internal::GetCapturedStdout();
+    if (verbose) std::cout << output;
+    ASSERT_EQ(lammps_has_error(lmp), 0);
+
+    EXPECT_DOUBLE_EQ(lammps_eval(lmp, "4+5"), 9.0);
+    EXPECT_EQ(lammps_has_error(lmp), 0);
+    EXPECT_DOUBLE_EQ(lammps_eval(lmp, "v_one / 2.0"), 0.5);
+    EXPECT_EQ(lammps_has_error(lmp), 0);
+    EXPECT_DOUBLE_EQ(lammps_eval(lmp, "count(all)"), 36.0);
+    EXPECT_EQ(lammps_has_error(lmp), 0);
+    EXPECT_DOUBLE_EQ(lammps_eval(lmp, "pe"), -3.9848867644689534);
+    EXPECT_EQ(lammps_has_error(lmp), 0);
+}

unittest/python/python-commands.py

@@ -538,6 +538,27 @@ create_atoms 1 single &
         expanded = self.lmp.expand("'xx_$(4+5)_$(PI) ${one}-${two}-${three}'")
         self.assertEqual(expanded, "'xx_$(4+5)_$(PI) ${one}-${two}-${three}'")
 
+    def test_eval(self):
+        self.lmp.commands_string(
+            """region box1 block 0 10 0 5 -0.5 0.5
+            lattice fcc 0.8
+            create_box 1 box1
+            create_atoms 1 box
+            mass * 1.0
+            pair_style lj/cut 4.0
+            pair_coeff * * 1.0 1.0
+            variable t equal 15.0
+            velocity all create 1.5 532656
+            fix 1 all nve
+            run 0 post no""")
+        self.lmp.command("variable one    index     1 2 3 4")
+        self.lmp.command("variable two    equal     2")
+
+        self.assertEqual(self.lmp.eval("4+5"), 9.0)
+        self.assertEqual(self.lmp.eval("v_one / 2.0"), 0.5)
+        self.assertEqual(self.lmp.eval("count(all)"), 36.0)
+        self.assertEqual(self.lmp.eval("pe"), -3.9848867644689534)
+
     def test_get_thermo(self):
         self.lmp.command("units lj")
         self.lmp.command("atom_style atomic")