Improve test coverage

test/trixi_include.jl

@@ -19,6 +19,10 @@
             @test_nowarn trixi_include(@__MODULE__, filename, x=7)
             @test x == 7
 
+            # Verify default version (that includes in `Main`)
+            @test_nowarn trixi_include(filename, x=11)
+            @test Main.x == 11
+
             @test_throws "assignment `y` not found in expression" trixi_include(@__MODULE__,
                                                                                 filename,
                                                                                 y=3)
@@ -58,6 +62,8 @@
         # We need another example file that we include with `Base.include` first, in order to
         # define the `solve` method without `trixi_include` trying to insert `maxiters` kwargs.
         # Then, we can test that `trixi_include` inserts the kwarg in the `solve()` call.
+        # Finally, we verify the logic that prevents adding multiple `maxiters` in case it
+        # is already present (either before or after the `;`)
         example1 = """
             solve(; maxiters=0) = maxiters
             """
@@ -66,15 +72,31 @@
             x = solve()
             """
 
+        example3 = """
+            y = solve(maxiters=0)
+            """
+
+        example4 = """
+            y = solve(; maxiters=0)
+            """
+
         filename1 = tempname()
         filename2 = tempname()
+        filename3 = tempname()
+        filename4 = tempname()
         try
             open(filename1, "w") do file
                 write(file, example1)
             end
             open(filename2, "w") do file
                 write(file, example2)
             end
+            open(filename3, "w") do file
+                write(file, example3)
+            end
+            open(filename4, "w") do file
+                write(file, example4)
+            end
 
             # Use `@trixi_testset`, which wraps code in a temporary module, and call
             # `Base.include` and `trixi_include` with `@__MODULE__` in order to isolate this test.
@@ -84,13 +106,22 @@
             # This is the default `maxiters` inserted by `trixi_include`
             @test x == 10^5
 
-            @test_nowarn trixi_include(@__MODULE__, filename2,
-                                       maxiters=7)
+            @test_nowarn trixi_include(@__MODULE__, filename2, maxiters=7)
             # Test that `maxiters` got overwritten
             @test x == 7
+
+            # Verify that adding `maxiters` to `maxiters` results in exactly one of them
+            # case 1) `maxiters` is *before* semicolon in included file
+            @test_nowarn trixi_include(@__MODULE__, filename3, maxiters=11)
+            @test y == 11
+            # case 2) `maxiters` is *after* semicolon in included file
+            @test_nowarn trixi_include(@__MODULE__, filename3, maxiters=14)
+            @test y == 14
         finally
             rm(filename1, force=true)
             rm(filename2, force=true)
+            rm(filename3, force=true)
+            rm(filename4, force=true)
         end
     end
 end