Add test case for trigonometric functions fix

Added comprehensive test for Issue #20 to verify that:
- sin(x) and cos(x) can be integrated with RischMethod() without errors
- Results are properly computed and returned as symbolic expressions
- Domain compatibility issues are resolved

The test is integrated into the main test suite under the Risch method tests.

Author: ChrisRackauckas

test/methods/risch/test_trigonometric_functions.jl

@@ -0,0 +1,25 @@
+using Test
+using SymbolicIntegration
+using Symbolics
+
+@testset "Trigonometric Functions with Risch Method" begin
+    @variables x
+    
+    @testset "Issue #20: Domain compatibility fix" begin
+        # Test that trigonometric functions can be integrated with RischMethod
+        # without throwing domain mismatch errors
+        
+        @test_nowarn integrate(sin(x), x, RischMethod())
+        @test_nowarn integrate(cos(x), x, RischMethod()) 
+        
+        # Test that the result is computed (not just that it doesn't error)
+        sin_result = integrate(sin(x), x, RischMethod())
+        cos_result = integrate(cos(x), x, RischMethod())
+        
+        # The results should not be nothing and should be symbolic expressions
+        @test sin_result !== nothing
+        @test cos_result !== nothing
+        @test sin_result isa Union{Number, SymbolicUtils.BasicSymbolic}
+        @test cos_result isa Union{Number, SymbolicUtils.BasicSymbolic}
+    end
+end

test/runtests.jl

@@ -21,6 +21,7 @@ using Symbolics
     # Include Risch method test suites
     include("methods/risch/test_rational_integration.jl")
     include("methods/risch/test_complex_fields.jl") 
+    include("methods/risch/test_trigonometric_functions.jl")
     include("methods/risch/test_bronstein_examples.jl")
     include("methods/risch/test_algorithm_internals.jl")