adding unit tests for to_lower, to_upper, reverse, to_title functions of stdlib_string_type module

Author: aman-godara

src/tests/string/test_string_functions.f90

@@ -0,0 +1,58 @@
+! SPDX-Identifier: MIT
+module test_string_functions
+    use stdlib_error, only : check
+    use stdlib_string_type, only : string_type, assignment(=), operator(==), &
+                                    to_lower, to_upper, to_title, reverse
+    implicit none
+
+contains
+
+    subroutine test_to_lower_string
+        type(string_type) :: test_string, compare_string
+        test_string = "To_LoWEr !$%-az09AZ"
+        compare_string = "to_lower !$%-az09az"
+
+        call check(to_lower(test_string) == compare_string)
+
+    end subroutine test_to_lower_string
+
+    subroutine test_to_upper_string
+        type(string_type) :: test_string, compare_string
+        test_string = "To_UpPeR !$%-az09AZ"
+        compare_string = "TO_UPPER !$%-AZ09AZ"
+
+        call check(to_upper(test_string) == compare_string)
+
+    end subroutine test_to_upper_string
+
+    subroutine test_to_title_string
+        type(string_type) :: test_string, compare_string
+        test_string = "_#To tiTlE !$%-az09AZ"
+        compare_string = "_#To title !$%-a09az"
+
+        call check(to_title(test_string) == compare_string)
+
+    end subroutine test_to_title_string
+
+    subroutine test_reverse_string
+        type(string_type) :: test_string, compare_string
+        test_string = "_To ReVerSe !$%-az09AZ   "
+        compare_string = "   ZA90za-%$! eSreVeR oT_"
+
+        call check(reverse(test_string) == compare_string)
+
+    end subroutine test_reverse_string
+
+end module test_string_functions
+
+
+program tester
+    use test_string_functions
+    implicit none
+
+    call test_to_lower_string
+    call test_to_upper_string
+    call test_to_title_string
+    call test_reverse_string
+
+end program tester