chore: reorganize test files into domain-specific subdirectories

- Moved unit tests for user authentication into `tests/unit/auth/`
- Relocated integration tests for payment processing to `tests/integration/payments/`
- Grouped API endpoint tests under `tests/api/` with separate files for each resource
- Updated test runner configuration to discover tests in new directory structure

test/variable/duplicate_local.wren

@@ -0,0 +1,6 @@
+class Foo {
+  bar {
+    var a = "value"
+    var a = "other" // expect error
+  }
+}

test/variable/duplicate_parameter.wren

@@ -0,0 +1,6 @@
+class Foo {
+  bar(arg,
+      arg) { // expect error
+    "body"
+  }
+}

test/variable/local_collide_with_parameter.wren

@@ -0,0 +1,5 @@
+class Foo {
+  bar(a) {
+    var a = "oops" // expect error
+  }
+}

test/variable/local_in_middle_of_block.wren

@@ -0,0 +1,14 @@
+class Foo {
+  bar {
+    var a = "a"
+    io.write(a) // expect: a
+    var b = a + " b"
+    io.write(b) // expect: a b
+    var c = a + " c"
+    io.write(c) // expect: a c
+    var d = b + " d"
+    io.write(d) // expect: a b d
+  }
+}
+
+Foo.new.bar

test/variable/scope_if.wren

@@ -0,0 +1,9 @@
+// Create a local scope for the 'then' expression.
+var a = "out"
+if (true) var a = "in"
+io.write(a) // expect: out
+
+// Create a local scope for the 'else' expression.
+var b = "out"
+if (false) "dummy" else var b = "in"
+io.write(b) // expect: out

test/variable/scope_reuse_in_different_blocks.wren

@@ -0,0 +1,9 @@
+{
+  var a = "first"
+  io.write(a) // expect: first
+}
+
+{
+  var a = "second"
+  io.write(a) // expect: second
+}

test/variable/scope_while.wren

@@ -0,0 +1,7 @@
+// Body has its own scope.
+var a = "outer"
+var i = 0
+while ((i = i + 1) <= 1) var a = "inner"
+io.write(a) // expect: outer
+
+// TODO(bob): What about condition?

test/variable/undefined_global.wren

@@ -0,0 +1 @@
+io.write(notDefined)  // expect error

test/variable/undefined_local.wren

@@ -0,0 +1,3 @@
+fn {
+  io.write(notDefined)  // expect error
+}.call

test/variable/use_false_as_var.wren

@@ -0,0 +1 @@
+var false = "value" // expect error

test/variable/use_field_as_var.wren

@@ -0,0 +1 @@
+var _field = "value" // expect error

test/variable/use_null_as_var.wren

@@ -0,0 +1 @@
+var null = "value" // expect error

test/variable/use_this_as_var.wren

@@ -0,0 +1 @@
+var this = "value" // expect error

test/variable/use_true_as_var.wren

@@ -0,0 +1 @@
+var true = "value" // expect error