ensure pycall has the right interpreter

Author: Christopher Doris

test/runtests.jl

@@ -1,12 +1,23 @@
+# build PyCall with the same interpreter as PythonCall
+using PythonCall: PythonCall
+using Pkg: Pkg
+ENV["PYTHON"] = PythonCall.python_executable_path()
+@info "Building PyCall..." ENV["PYTHON"]
+Pkg.build("PyCall")
+
 using TestItemRunner
 
 @run_package_tests
 
 @testmodule PyCall begin
+    # build PyCall with the same interpreter as PythonCall
     using PythonCall: PythonCall
-    using Pkg: Pkg
-    ENV["PYTHON"] = PythonCall.python_executable_path()
-    @info "Building PyCall..." ENV["PYTHON"]
-    Pkg.build("PyCall")
+    if get(ENV, "PYTHON", "") != PythonCall.python_executable_path()
+        # ... but only if we didn't already do this
+        using Pkg: Pkg
+        ENV["PYTHON"] = PythonCall.python_executable_path()
+        @info "Building PyCall..." ENV["PYTHON"]
+        Pkg.build("PyCall")
+    end
     using PyCall
 end