Reorganize tests and benchmark scripts.

Mainly to get rid of one top level directory. But this will
also be useful when there are tests of the embedding API.

test/language/assignment/associativity.wren

@@ -0,0 +1,9 @@
+var a = "a"
+var b = "b"
+var c = "c"
+
+// Assignment is right-associative.
+a = b = c
+IO.print(a) // expect: c
+IO.print(b) // expect: c
+IO.print(c) // expect: c

test/language/assignment/global.wren

@@ -0,0 +1,8 @@
+var a = "before"
+IO.print(a) // expect: before
+
+a = "after"
+IO.print(a) // expect: after
+
+IO.print(a = "arg") // expect: arg
+IO.print(a) // expect: arg

test/language/assignment/grouping.wren

@@ -0,0 +1,2 @@
+var a = "a"
+(a) = "value" // expect error

test/language/assignment/infix_operator.wren

@@ -0,0 +1,3 @@
+var a = "a"
+var b = "b"
+a + b = "value" // expect error

test/language/assignment/is.wren

@@ -0,0 +1,3 @@
+var a = "a"
+var b = "b"
+b is a = "value" // expect error

test/language/assignment/local.wren

@@ -0,0 +1,10 @@
+new Fn {
+  var a = "before"
+  IO.print(a) // expect: before
+
+  a = "after"
+  IO.print(a) // expect: after
+
+  IO.print(a = "arg") // expect: arg
+  IO.print(a) // expect: arg
+}.call()

test/language/assignment/prefix_operator.wren

@@ -0,0 +1,2 @@
+var a = "a"
+!a = "value" // expect error

test/language/assignment/syntax.wren

@@ -0,0 +1,11 @@
+// Chained assignment.
+var a = "a"
+var b = "b"
+a = b = "chain"
+IO.print(a) // expect: chain
+IO.print(a) // expect: chain
+
+// Assignment on RHS of variable.
+var c = a = "var"
+IO.print(a) // expect: var
+IO.print(c) // expect: var

test/language/assignment/undefined.wren

@@ -0,0 +1 @@
+unknown = "what" // expect error