fix: Standardize precision alias in tests to wp (fixes #1343) (#1344)

Summary
- Replace direct real64/dp usage in selected tests with wp alias for
consistency with src/.
- Tighten imports to follow project style (`use <module>, only:`) and
source `wp` from `fortplot`.

Changes
- test/test_streamplot_interface_color.f90: use `wp` from `fortplot`;
keep advanced API imports.
- test/test_streamplot_arrows.f90: switch to explicit `fortplot` imports
(`figure, streamplot, title, savefig, wp`).
- test/test_png_file_size_scaling.f90: already used `wp` from `fortplot`
(no change).
- test/test_scatter_color_cycle.f90: import `wp` from `fortplot`
alongside `figure_t`.

Rationale
- Align tests with repository guidelines:
- Prefer `use fortplot, only: wp => real64` over intrinsic wp wiring in
tests.
- Use explicit-only imports for clarity and to prevent namespace bleed.

Verification (local)
Commands run from repository root:
- make test-ci
- Project compiled successfully; CI essential test suite completed
successfully.
  - Sample excerpt: "CI essential test suite completed successfully".
- make verify-artifacts
  - Artifact verification passed.
  - Sample excerpts:
    - "[ok] symlog ylabel shows superscript three (unicode)"
- "[ok] output/example/fortran/pcolormesh_demo/pcolormesh_basic.pdf
contains RGB Image XObject"
    - "Artifact verification passed."

Artifacts
- Example outputs unchanged under `output/` and
`output/example/fortran/`. No rendering changes expected.

Notes
- Keeps functions small and focused; no behavioral changes, only
style/consistency.

Author: krystophny

test/test_png_file_size_scaling.f90

@@ -2,7 +2,6 @@ program test_png_file_size_scaling
     !! Test that PNG files scale appropriately with content complexity
     use fortplot, only: figure_t, wp
     use fortplot_logging, only: set_log_level, LOG_LEVEL_ERROR
-    use, intrinsic :: iso_fortran_env, only: real64
     implicit none
 
     integer :: simple_size, complex_size, empty_size
@@ -78,13 +77,13 @@ end subroutine test_empty_plot
     subroutine test_simple_plot(file_size)
         integer, intent(out) :: file_size
         type(figure_t) :: plt
-        real(real64), allocatable :: x(:), y(:)
+        real(wp), allocatable :: x(:), y(:)
         character(len=256) :: output_dir, filename
 
         call get_output_directory(output_dir)
         call plt%initialize(800, 600)  ! Medium size
 
-        x = create_linspace(0.0_real64, 10.0_real64, 10)
+        x = create_linspace(0.0_wp, 10.0_wp, 10)
         allocate(y(10))
         y = x
 
@@ -100,21 +99,21 @@ end subroutine test_simple_plot
     subroutine test_complex_plot(file_size)
         integer, intent(out) :: file_size
         type(figure_t) :: plt
-        real(real64), allocatable :: x(:), y1(:), y2(:), y3(:)
+        real(wp), allocatable :: x(:), y1(:), y2(:), y3(:)
         character(len=256) :: output_dir, filename
         integer :: i
 
         call get_output_directory(output_dir)
         call plt%initialize(1600, 1200)  ! Large size for more data
 
-        x = create_linspace(0.0_real64, 10.0_real64, 5000)  ! More data points
+        x = create_linspace(0.0_wp, 10.0_wp, 5000)  ! More data points
         allocate(y1(5000), y2(5000), y3(5000))
 
         ! Add multiple complex lines with high-frequency patterns
         do i = 1, size(x)
-            y1(i) = sin(x(i) * 10.0_real64) * cos(x(i) * 20.0_real64)
-            y2(i) = exp(-x(i)/5.0_real64) * sin(x(i) * 15.0_real64)
-            y3(i) = sin(x(i) * 30.0_real64) * cos(x(i) * 25.0_real64)
+            y1(i) = sin(x(i) * 10.0_wp) * cos(x(i) * 20.0_wp)
+            y2(i) = exp(-x(i)/5.0_wp) * sin(x(i) * 15.0_wp)
+            y3(i) = sin(x(i) * 30.0_wp) * cos(x(i) * 25.0_wp)
         end do
 
         call plt%add_plot(x, y1, label='High-frequency oscillation 1')
@@ -193,22 +192,22 @@ end function get_file_size
 
     function create_linspace(start, stop, n) result(arr)
         !! Create linearly spaced array from start to stop with n points
-        real(real64), intent(in) :: start, stop
+        real(wp), intent(in) :: start, stop
         integer, intent(in) :: n
-        real(real64), allocatable :: arr(:)
+        real(wp), allocatable :: arr(:)
         integer :: i
-        real(real64) :: dx
+        real(wp) :: dx
 
         allocate(arr(n))
 
         if (n == 1) then
             arr(1) = start
         else
-            dx = (stop - start) / real(n - 1, real64)
+            dx = (stop - start) / real(n - 1, wp)
             do i = 1, n
-                arr(i) = start + real(i - 1, real64) * dx
+                arr(i) = start + real(i - 1, wp) * dx
             end do
         end if
     end function create_linspace
 
-end program test_png_file_size_scaling
+end program test_png_file_size_scaling

test/test_scatter_color_cycle.f90

@@ -1,20 +1,19 @@
 program test_scatter_color_cycle
     !! Verify scatter plots share the default color cycle with line plots
-    use, intrinsic :: iso_fortran_env, only: dp => real64
-    use fortplot, only: figure_t
+    use fortplot, only: figure_t, wp
     use fortplot_figure_plot_management, only: next_plot_color
     implicit none
 
     type(figure_t) :: fig
-    real(dp) :: x(5), y_line(5), y_scatter(5)
-    real(dp) :: expected_color(3)
-    real(dp) :: scatter_color(3)
+    real(wp) :: x(5), y_line(5), y_scatter(5)
+    real(wp) :: expected_color(3)
+    real(wp) :: scatter_color(3)
 
     integer :: i
 
-    x = [(real(i, dp), i = 1, size(x))]
+    x = [(real(i, wp), i = 1, size(x))]
     y_line = x
-    y_scatter = x + 1.0_dp
+    y_scatter = x + 1.0_wp
 
     call fig%initialize()
 
@@ -26,7 +25,7 @@ program test_scatter_color_cycle
 
     scatter_color = fig%plots(fig%plot_count)%color
 
-    if (any(abs(scatter_color - expected_color) > 1.0e-12_dp)) then
+    if (any(abs(scatter_color - expected_color) > 1.0e-12_wp)) then
         print *, 'FAIL: scatter default color diverged from shared cycle'
         print *, '  expected:', expected_color
         print *, '  actual  :', scatter_color

test/test_streamplot_arrows.f90

@@ -1,12 +1,11 @@
 program test_streamplot_arrows
     !! Verify streamplot arrow rendering via matplotlib-style wrapper
-    use fortplot
-    use, intrinsic :: iso_fortran_env, only: real64
+    use fortplot, only: figure, streamplot, title, savefig, wp
     use test_output_helpers, only: ensure_test_output_dir
     implicit none
 
-    real(real64), allocatable :: x(:), y(:)
-    real(real64), allocatable :: u(:,:), v(:,:)
+    real(wp), allocatable :: x(:), y(:)
+    real(wp), allocatable :: u(:,:), v(:,:)
     character(len=:), allocatable :: outdir
     integer :: i, j, nx, ny
 
@@ -16,22 +15,22 @@ program test_streamplot_arrows
     allocate(x(nx), y(ny), u(nx, ny), v(nx, ny))
 
     do i = 1, nx
-        x(i) = real(i-1, real64) / real(nx-1, real64)
+        x(i) = real(i-1, wp) / real(nx-1, wp)
     end do
     do j = 1, ny
-        y(j) = real(j-1, real64) / real(ny-1, real64)
+        y(j) = real(j-1, wp) / real(ny-1, wp)
     end do
 
     ! Simple rotational field
     do j = 1, ny
         do i = 1, nx
-            u(i,j) = -(y(j) - 0.5_real64)
-            v(i,j) =  (x(i) - 0.5_real64)
+            u(i,j) = -(y(j) - 0.5_wp)
+            v(i,j) =  (x(i) - 0.5_wp)
         end do
     end do
 
     call figure()
-    call streamplot(x, y, u, v, density=1.0_real64, arrowsize=1.0_real64, arrowstyle='->')
+    call streamplot(x, y, u, v, density=1.0_wp, arrowsize=1.0_wp, arrowstyle='->')
     call title('streamplot arrows smoke test')
     call savefig(trim(outdir)//'streamplot_arrows.png')
 

test/test_streamplot_interface_color.f90

@@ -1,28 +1,28 @@
 program test_streamplot_interface_color
-    use, intrinsic :: iso_fortran_env, only: real64
+    use fortplot, only: wp
     use fortplot_matplotlib_advanced, only: streamplot, get_global_figure, ensure_global_figure_initialized
     use fortplot_figure_core, only: figure_t
     use fortplot_plot_data, only: plot_data_t
     implicit none
 
-    real(real64), dimension(5) :: x
-    real(real64), dimension(5) :: y
-    real(real64), dimension(5,5) :: u, v
+    real(wp), dimension(5) :: x
+    real(wp), dimension(5) :: y
+    real(wp), dimension(5,5) :: u, v
     class(figure_t), pointer :: fig
     type(plot_data_t), pointer :: plots(:)
     integer :: i, j, n
-    real(real64), dimension(3) :: ref_color
+    real(wp), dimension(3) :: ref_color
     logical :: all_same
 
     ! Setup a simple vector field
     do i = 1, 5
-        x(i) = real(i-1, real64)
-        y(i) = real(i-1, real64)
+        x(i) = real(i-1, wp)
+        y(i) = real(i-1, wp)
     end do
     do j = 1, 5
         do i = 1, 5
-            u(i,j) = 1.0_real64
-            v(i,j) = 0.0_real64
+            u(i,j) = 1.0_wp
+            v(i,j) = 0.0_wp
         end do
     end do
 
@@ -40,7 +40,7 @@ program test_streamplot_interface_color
     ref_color = plots(1)%color
     all_same = .true.
     do i = 2, n
-        if (any(abs(plots(i)%color - ref_color) > 1.0e-12_real64)) then
+        if (any(abs(plots(i)%color - ref_color) > 1.0e-12_wp)) then
             all_same = .false.
             exit
         end if
@@ -52,11 +52,10 @@ program test_streamplot_interface_color
     end if
 
     ! Optional: check equals default blue
-    if (any(abs(ref_color - [0.0_real64, 0.447_real64, 0.698_real64]) > 1.0e-12_real64)) then
+    if (any(abs(ref_color - [0.0_wp, 0.447_wp, 0.698_wp]) > 1.0e-12_wp)) then
         print *, "ERROR: Streamplot default color not blue as expected"
         stop 1
     end if
 
     print *, "Streamplot interface color test passed"
 end program test_streamplot_interface_color
-