test(tests/poly): poly solver test

added test for the polytropic solver (which is also being used to validate and confirm it works)

tests/poly/polyTest.cpp

@@ -6,4 +6,9 @@ class polyTest : public ::testing::Test {};
 
 TEST_F(polyTest, DefaultConstructor) {
     EXPECT_NO_THROW(PolySolver(1, 1));
+}
+
+TEST_F(polyTest, Solve) {
+    PolySolver polytrope(1.5, 1);
+    EXPECT_NO_THROW(polytrope.solve());
 }