Improve unit test coverage

[GV14982]

I think it would be smart to setup tests for as many individual functions as possible. This will likely be an ongoing effort.

[GV14982]

Current functions with no tests:

• src/errors.gleam:68 - map_lex_to_parse_error
• src/internal/executable/operation/executable.gleam:16 - make_executable
• src/internal/executable/schema/executable.gleam:35 - from_types

Schema Merging & Type System (33 functions)

• src/internal/executable/schema/merge.gleam:24 - merge_schema
• src/internal/executable/schema/merge.gleam:53 - merge_types
• src/internal/executable/schema/merge.gleam:72 - merge_scalar
• src/internal/executable/schema/merge.gleam:90 - merge_object
• src/internal/executable/schema/merge.gleam:176 - merge_input
• src/internal/executable/schema/merge.gleam:227 - merge_interface
• src/internal/executable/schema/merge.gleam:317 - merge_union
• src/internal/executable/schema/merge.gleam:360 - merge_enum
• src/internal/executable/schema/type_system.gleam:42 - from_schema_doc
• src/internal/executable/schema/type_system.gleam:78 - type_ext
• src/internal/executable/schema/type_system.gleam:185 - type_node
• src/internal/executable/schema/type_system.gleam:275 - map_directives
• src/internal/executable/schema/type_system.gleam:291 - map_fields
• src/internal/executable/schema/type_system.gleam:317 - map_input_values
• src/internal/executable/schema/type_system.gleam:342 - map_enum_members
• src/internal/executable/schema/type_system.gleam:353 - map_named_type_nodes
• src/internal/executable/schema/type_system.gleam:360 - map_type_node
• src/internal/executable/schema/type_system.gleam:385 - map_const_value
• src/internal/executable/schema/type_system.gleam:403 - map_const
• src/internal/executable/schema/type_system.gleam:415 - get_root_operation

Lexer Functions (20 functions)

• src/internal/lexer/lexer.gleam:33 - lex_until_error
• src/internal/lexer/lexer.gleam:49 - lookahead
• src/internal/lexer/lexer.gleam:54 - get_next_token
• src/internal/lexer/lexer.gleam:167 - handle_name_or_number
• src/internal/lexer/lexer.gleam:208 - consume_comment
• src/internal/lexer/lexer.gleam:224 - consume_name
• src/internal/lexer/lexer.gleam:244 - consume_string
• src/internal/lexer/lexer.gleam:271 - consume_block_string
• src/internal/lexer/lexer.gleam:306 - consume_number
• src/internal/lexer/lexer.gleam:337 - number_type_to_token_kind
• src/internal/lexer/position.gleam:8 - new
• src/internal/lexer/position.gleam:12 - inc_col_by
• src/internal/lexer/position.gleam:17 - inc_row
• src/internal/lexer/predicates.gleam:1 - is_ignored
• src/internal/lexer/predicates.gleam:8 - is_name
• src/internal/lexer/predicates.gleam:12 - is_name_start
• src/internal/lexer/predicates.gleam:16 - is_alphanumeric
• src/internal/lexer/predicates.gleam:20 - is_digit
• src/internal/lexer/predicates.gleam:24 - is_non_zero_digit
• src/internal/lexer/predicates.gleam:31 - is_alpha
• src/internal/lexer/predicates.gleam:35 - is_upper
• src/internal/lexer/predicates.gleam:67 - is_lower

Parser Functions (64 functions)

Argument Parsing

• src/internal/parser/arg.gleam:11 - parse_optional_args
• src/internal/parser/arg.gleam:29 - parse_arg_list
• src/internal/parser/arg.gleam:47 - parse_arg
• src/internal/parser/arg.gleam:63 - parse_var_or_const
• src/internal/parser/arg.gleam:107 - parse_list_value
• src/internal/parser/arg.gleam:124 - parse_object_field
• src/internal/parser/arg.gleam:140 - parse_object_value

Constant Parsing

• src/internal/parser/const_arg_def.gleam:11 - parse_optional_const_arg_defs
• src/internal/parser/const_directive.gleam:12 - parse_optional_const_directive_list
• src/internal/parser/const_directive.gleam:38 - parse_optional_const_directive
• src/internal/parser/const_value.gleam:11 - parse_const_value
• src/internal/parser/const_value.gleam:34 - parse_const
• src/internal/parser/default_value.gleam:9 - parse_optional

Directive Parsing

• src/internal/parser/directive.gleam:12 - parse_optional_directive_list
• src/internal/parser/directive.gleam:38 - parse_optional_directive

Type & Utility Parsing

• src/internal/parser/named_type.gleam:9 - parse_named_type_list
• src/internal/parser/type_node.gleam:7 - parse_type_node
• src/internal/parser/util.gleam:10 - expect_next
• src/internal/parser/util.gleam:21 - parse_between
• src/internal/parser/util.gleam:44 - parse_between_optional
• src/internal/parser/util.gleam:65 - parse_until

Operation Parsing

• src/internal/parser/operation/definition.gleam:9 - parse_operation
• src/internal/parser/operation/fragment_def.gleam:10 - parse_fragment_def
• src/internal/parser/operation/operation_def.gleam:12 - parse_operation_def
• src/internal/parser/operation/operation_def.gleam:31 - parse_unnamed_operation
• src/internal/parser/operation/operation_def.gleam:54 - parse_named_operation
• src/internal/parser/operation/selection_set.gleam:12 - parse_field_name
• src/internal/parser/operation/selection_set.gleam:47 - parse_field
• src/internal/parser/operation/selection_set.gleam:76 - parse_optional_selection_set
• src/internal/parser/operation/selection_set.gleam:96 - parse_selection_set
• src/internal/parser/operation/selection_set.gleam:116 - parse_selection
• src/internal/parser/operation/selection_set.gleam:158 - parse_optional_named_type_spread
• src/internal/parser/operation/selection_set.gleam:174 - parse_selections
• src/internal/parser/operation/variable_def.gleam:12 - parse_optional_variable_definitions
• src/internal/parser/operation/variable_def.gleam:29 - parse_variable_definition_list

Schema Parsing

• src/internal/parser/schema/definition.gleam:17 - parse
• src/internal/parser/schema/definition.gleam:86 - parse_type_ext
• src/internal/parser/schema/definition.gleam:104 - parse_type_def
• src/internal/parser/schema/description.gleam:7 - parse_optional_description
• src/internal/parser/schema/directive_def.gleam:11 - parse_directive_def
• src/internal/parser/schema/directive_def.gleam:57 - parse_directive_locations
• src/internal/parser/schema/directive_def.gleam:87 - parse_directive_location
• src/internal/parser/schema/enum.gleam:13 - parse_enum_ext
• src/internal/parser/schema/enum.gleam:56 - parse_enum_def
• src/internal/parser/schema/enum.gleam:86 - parse_optional_enum_members_def
• src/internal/parser/schema/enum.gleam:102 - parse_enum_members_def
• src/internal/parser/schema/enum.gleam:119 - parse_enum_member_list
• src/internal/parser/schema/enum.gleam:151 - parse_enum_member
• src/internal/parser/schema/field_def.gleam:14 - parse_optional_field_definitions
• src/internal/parser/schema/field_def.gleam:28 - parse_field_definition
• src/internal/parser/schema/input_def.gleam:11 - parse_input_ext
• src/internal/parser/schema/input_def.gleam:58 - parse_input_def
• src/internal/parser/schema/input_value_def.gleam:14 - parse_optional_input_value_def_list
• src/internal/parser/schema/input_value_def.gleam:27 - parse_input_value_def_list
• src/internal/parser/schema/input_value_def.gleam:46 - parse_input_value
• src/internal/parser/schema/interface.gleam:12 - parse_interface_ext
• src/internal/parser/schema/interface.gleam:71 - parse_interface_def
• src/internal/parser/schema/interface.gleam:105 - parse_optional_interface_implementations
• src/internal/parser/schema/object_def.gleam:12 - parse_object_ext
• src/internal/parser/schema/object_def.gleam:68 - parse_object_def
• src/internal/parser/schema/scalar.gleam:10 - parse_scalar_ext
• src/internal/parser/schema/scalar.gleam:38 - parse_scalar_def
• src/internal/parser/schema/schema_def.gleam:11 - parse_schema_extension
• src/internal/parser/schema/schema_def.gleam:52 - parse_schema_definition
• src/internal/parser/schema/union.gleam:11 - parse_union_ext
• src/internal/parser/schema/union.gleam:52 - parse_union_def

Utility Functions

• src/internal/util.gleam:3 - operation_type_to_string

Validation Functions (17 functions)

• src/internal/validate/schema/arg.gleam:24 - validate_arguments
• src/internal/validate/schema/directive.gleam:112 - validate_directive
• src/internal/validate/schema/directive.gleam:135 - validate_directive_location
• src/internal/validate/schema/field.gleam:24 - validate_field_definitions
• src/internal/validate/schema/field.gleam:58 - validate_field_type
• src/internal/validate/schema/input_field.gleam:24 - validate_input_field_definitions
• src/internal/validate/schema/input_field.gleam:62 - validate_input_field_type
• src/internal/validate/schema/names.gleam:24 - validate_unique_names
• src/internal/validate/schema/root_operations.gleam:25 - validate_root_operations
• src/internal/validate/schema/value.gleam:8 - validate_value_to_def
• src/internal/validate/schema/value.gleam:47 - validate_scalar_type
• src/internal/validate/schema/value.gleam:90 - validate_input_field_values
• src/internal/validate/schema/value.gleam:108 - get_scalar_name
• src/internal/validate/util.gleam:3 - is_nullable