Add new custom number type test

src/check/test/custom_num_type_test.zig

@@ -0,0 +1,70 @@
+//! Tests for custom number types that implement from_int_digits or from_dec_digits
+
+const std = @import("std");
+const TestEnv = @import("./TestEnv.zig");
+
+test "Custom number type with from_int_digits: integer literal unifies" {
+    const source =
+        \\{
+        \\  MyNum := [].{
+        \\    from_int_digits : List(U8) -> Try(MyNum, [OutOfRange])
+        \\    from_int_digits = |_| Err(OutOfRange)
+        \\  }
+        \\
+        \\  x : MyNum
+        \\  x = 42
+        \\
+        \\  x
+        \\}
+    ;
+
+    var test_env = try TestEnv.initExpr("Test", source);
+    defer test_env.deinit();
+
+    // Should type-check successfully - MyNum has from_int_digits so it can accept integer literals
+    try test_env.assertNoErrors();
+}
+
+test "Custom number type with from_dec_digits: decimal literal unifies" {
+    const source =
+        \\{
+        \\  MyDecimal := [].{
+        \\    from_dec_digits : { before_dot : List(U8), after_dot : List(U8) } -> Try(MyDecimal, [OutOfRange])
+        \\    from_dec_digits = |_| Err(OutOfRange)
+        \\  }
+        \\
+        \\  x : MyDecimal
+        \\  x = 3.14
+        \\
+        \\  x
+        \\}
+    ;
+
+    var test_env = try TestEnv.initExpr("Test", source);
+    defer test_env.deinit();
+
+    // Should type-check successfully - MyDecimal has from_dec_digits so it can accept decimal literals
+    try test_env.assertNoErrors();
+}
+
+test "Custom number type without from_int_digits: integer literal does not unify" {
+    const source =
+        \\{
+        \\  MyType := [].{
+        \\    some_method : MyType -> Bool
+        \\    some_method = |_| True
+        \\  }
+        \\
+        \\  x : MyType
+        \\  x = 42
+        \\
+        \\  x
+        \\}
+    ;
+
+    var test_env = try TestEnv.initExpr("Test", source);
+    defer test_env.deinit();
+
+    // Should fail - MyType doesn't have from_int_digits
+    try test_env.assertOneTypeError("TYPE MISMATCH");
+}