Add solution for temp conversions exercise

Author: connoraird

episodes/6-writing-your-first-unit-test/standard-fortran/challenge/README.md

@@ -6,7 +6,7 @@ Fortran without the use of a testing framework, in order to teach the principles
 
 ## The src code
 
-in [src](./src) you will find a library [temp_conversions.f90](./src/temp_conversions.f90)
+In [src](./src) you will find a library [temp_conversions.f90](./src/temp_conversions.f90)
 which provides functions for converting between various units of temperature. The functions
 provided are...
 

episodes/6-writing-your-first-unit-test/standard-fortran/challenge/test/test_temp_conversions.f90

@@ -35,6 +35,6 @@ subroutine test(passed, failure_message)
 
         ! Populate the failure message
         write(failure_message, '(A,A)') "It is useful to include input, expected output and actual output values here. To do ", &
-                                        "that, replace (A,A) with the correct format for your values, for example (A,I3,A,I3,A,I3)."
+                                        "that, replace (A,A) with the correct format for your values, for example (A,F7.2,A,F7.2,A,F7.2)."
     end subroutine test
 end program test_temp_conversions

episodes/6-writing-your-first-unit-test/standard-fortran/solution/README.md

@@ -0,0 +1,38 @@
+# Writing your first unit test - Standard Fortran - Solution
+
+The solution is provided in the form of a single test file [test_temp_conversions.f90](./test_temp_conversions.f90)
+which replaces the file of the same name provided in the [challenge/test](../challenge/test/) directory.
+
+## Key points
+
+There are several key aspects within the solution that are important to implement in any test.
+
+### Isolated test subroutine
+
+Each test subroutine in [test_temp_conversions.f90](./test_temp_conversions.f90) calls and tests only one src
+function. For example, `test_fahrenheit_to_celsius` calls and tests `fahrenheit_to_celsius` and
+`test_celsius_to_kelvin` calls and tests `celsius_to_kelvin`.
+
+This is important as, in the event of a test failing it will be clear which src function is the cause of the failure.
+If instead we had implemented a single test subroutine which calls both `test_fahrenheit_to_celsius` and
+`fahrenheit_to_celsius`, then a failure in such a test could have been caused by either of those src functions and further
+investigation would be required.
+
+### Parameterised tests
+
+Each test subroutine in [test_temp_conversions.f90](./test_temp_conversions.f90) take in an `input` and an `expected_output`.
+This allows the same test subroutine to be called with multiple different inputs to test several scenarios with the same test
+code. Therefore, we are able to test edge cases and other key scenarios more easily.
+
+### Clear failure message
+
+Each test subroutine in [test_temp_conversions.f90](./test_temp_conversions.f90) populates `failure_message` with a clear
+message that aims to make it as easy as possible to diagnose a failing test. Importantly, the `failure_message` includes the
+`input`, the `expected_output` and the actual value which we have compared to the `expected_output`.
+
+### Comparing floats within an appropriate tolerance
+
+We cannot compare two floats directly as due to rounding errors they will almost always
+not be exactly the same. Therefore, we must check the difference between two floats that
+we expect to be equal and ensure it is less than some appropriate tolerance. This tolerance
+should be as small as possible whilst still making sense with the code we are testing.

episodes/6-writing-your-first-unit-test/standard-fortran/solution/test_temp_conversions.f90

@@ -0,0 +1,82 @@
+program test_temp_conversions
+    use temp_conversions, only : fahrenheit_to_celsius, celsius_to_kelvin
+    implicit none
+
+    ! The tolerance to use when comparing floats
+    real, parameter :: tolerance = 1e-6
+
+    integer :: i
+
+    ! Declare passed and failure message arrays to be set by a test subroutine(s)
+    logical :: passed(7)
+    character(len=200) :: failure_message(7)
+
+    call test_fahrenheit_to_celsius(0.0, -17.77778, passed(1), failure_message(1))
+    call test_fahrenheit_to_celsius(32.0, 0.0, passed(2), failure_message(2))
+    call test_fahrenheit_to_celsius(-100.0, -73.33, passed(3), failure_message(3))
+    call test_fahrenheit_to_celsius(1.23,-17.09, passed(4), failure_message(4))
+
+    call test_celsius_to_kelvin(0.0, 273.15, passed(5), failure_message(5))
+    call test_celsius_to_kelvin(-273.15, 0.0, passed(6), failure_message(6))
+    call test_celsius_to_kelvin(-173.15, 100.0, passed(7), failure_message(7))
+
+    if (all(passed)) then
+        write(*,*) "All tests passed!"
+    else
+      do i = 1, size(passed)
+          if (.not. passed(i)) then
+              write(*,*) "FAIL: ", trim(failure_message(i))
+          end if
+      end do
+      stop 1
+    end if
+
+contains
+    !> Unit test subroutine for celsius_to_kelvin
+    subroutine test_fahrenheit_to_celsius(input, expected_output, passed, failure_message)
+        !> The input fahrenheit value to pass to fahrenheit_to_celsius
+        real, intent(in) :: input
+        !> The celsius value we expect to be returner from fahrenheit_to_celsius
+        real, intent(in) :: expected_output
+        !> A logical to track whether the test passed or not
+        logical, intent(out) :: passed
+        !> A failure message to be displayed if passed is false
+        character(len=200), intent(out) :: failure_message
+
+        real :: actual_output
+
+        ! Get the actual celsius value returned from fahrenheit_to_celsius
+        actual_output = fahrenheit_to_celsius(input)
+
+        ! Check that the actual value is within some tolerance of the expected value
+        passed = abs(actual_output - expected_output) < tolerance
+
+        ! Populate the failure message
+        write(failure_message, '(A,F7.2,A,F7.2,A,F7.2)') "Failed With ", input, ": Expected ", expected_output, " but got ", &
+                                                 actual_output
+    end subroutine test_fahrenheit_to_celsius
+
+    !> Unit test subroutine for celsius_to_kelvin
+    subroutine test_celsius_to_kelvin(input, expected_output, passed, failure_message)
+        !> The input celsius value to pass to celsius_to_kelvin
+        real, intent(in) :: input
+        !> The kelvin value we expect to be returner from celsius_to_kelvin
+        real, intent(in) :: expected_output
+        !> A logical to track whether the test passed or not
+        logical, intent(out) :: passed
+        !> A failure message to be displayed if passed is false
+        character(len=200), intent(out) :: failure_message
+
+        real :: actual_output
+
+        ! Get the actual celsius value returned from celsius_to_kelvin
+        actual_output = celsius_to_kelvin(input)
+
+        ! Check that the actual value is within some tolerance of the expected value
+        passed = abs(actual_output - expected_output) < tolerance
+
+        ! Populate the failure message
+        write(failure_message, '(A,F7.2,A,F7.2,A,F7.2)') "Failed With ", input, ": Expected ", expected_output, " but got ", &
+                                                 actual_output
+    end subroutine test_celsius_to_kelvin
+end program test_temp_conversions