Replace use of nthreads() in tests

Author: penelopeysm

test/compiler.jl

@@ -606,7 +606,7 @@ module Issue537 end
         @model demo() = return __varinfo__
         retval, svi = DynamicPPL.init!!(demo(), SimpleVarInfo())
         @test svi == SimpleVarInfo()
-        if Threads.nthreads() > 1
+        if DynamicPPL.USE_THREADSAFE_EVAL[]
             @test retval isa DynamicPPL.ThreadSafeVarInfo{<:SimpleVarInfo}
             @test retval.varinfo == svi
         else

test/fasteval.jl

@@ -96,7 +96,7 @@ end
 end
 
 @testset "FastLDF: performance" begin
-    if Threads.nthreads() == 1
+    if !(DynamicPPL.USE_THREADSAFE_EVAL[])
         # Evaluating these three models should not lead to any allocations (but only when
         # not using TSVI).
         @model function f()

test/threadsafe.jl

@@ -64,6 +64,7 @@
 
     @testset "model" begin
         println("Peforming threading tests with $(Threads.nthreads()) threads")
+        @show DynamicPPL.USE_THREADSAFE_EVAL[]
 
         x = rand(10_000)
 
@@ -79,10 +80,10 @@
         vi = VarInfo()
         model(vi)
         lp_w_threads = getlogjoint(vi)
-        if Threads.nthreads() == 1
-            @test vi_ isa VarInfo
-        else
+        if DynamicPPL.USE_THREADSAFE_EVAL[]
             @test vi_ isa DynamicPPL.ThreadSafeVarInfo
+        else
+            @test vi_ isa VarInfo
         end
 
         println("With `@threads`:")
@@ -112,10 +113,10 @@
         vi = VarInfo()
         model(vi)
         lp_wo_threads = getlogjoint(vi)
-        if Threads.nthreads() == 1
-            @test vi_ isa VarInfo
-        else
+        if DynamicPPL.USE_THREADSAFE_EVAL[]
             @test vi_ isa DynamicPPL.ThreadSafeVarInfo
+        else
+            @test vi_ isa VarInfo
         end
 
         println("Without `@threads`:")