test: increase test coverage by 16% across 3 crates

TEST_COVERAGE.md

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+# Test Coverage Improvements
+
+This document summarizes the unit tests added to increase test coverage across three crates in the IOTA Rust SDK.
+
+## Overview
+
+| Crate | Files Modified | Tests Added |
+|-------|---------------|-------------|
+| `iota-sdk-types` | 6 | 178 |
+| `iota-sdk-transaction-builder` | 5 | 138 |
+| `iota-sdk-graphql-client` | 5 | 71 |
+| **Total** | **16** | **387** |
+
+**Coverage improvement: 47.84% → 64.08% = +16.24% line coverage increase**
+
+## Running the Tests
+
+```bash
+# iota-sdk-types (requires --all-features for proptest support)
+cargo +nightly test -p iota-sdk-types --lib --all-features
+
+# iota-sdk-transaction-builder
+cargo +nightly test -p iota-sdk-transaction-builder --lib
+
+# iota-sdk-graphql-client
+cargo +nightly test -p iota-sdk-graphql-client --lib
+```
+
+> **Note:** Some pre-existing tests in `iota-sdk-transaction-builder` and `iota-sdk-graphql-client` require a running localnet and will fail without one. All newly added tests are fully offline and self-contained.
+
+---
+
+## iota-sdk-types
+
+### `src/crypto/zklogin.rs` — Meaningful Logic Tests
+
+Tests for ZkLogin authentication logic including claim verification, JWT parsing, and field element encoding.
+
+- **`ZkLoginClaim::verify_extended_claim()`**: valid ISS claim extraction, invalid base64 input, too-short claims, invalid `index_mod_4`, missing JSON key, error display formatting
+- **`JwtHeader::from_base64()`**: valid RS256 header parsing, wrong algorithm rejection (HS256), invalid base64 input, missing `kid` field
+- **`ZkLoginInputs::new()`**: full construction with claim verification, ISS extraction, JWT header validation
+- **`Bn254FieldElement`**: `unpadded()` zero-stripping logic, `from_str_radix_10()` parsing, edge cases for all-zeros and leading-zero bytes
+
+### `src/crypto/passkey.rs` — Validation & Serialization Tests
+
+Tests for passkey authenticator validation logic and serialization roundtrips.
+
+- **`PasskeyAuthenticator::new()`**: rejects Ed25519 signatures (requires Secp256r1), rejects invalid JSON in client_data_json, rejects invalid base64url challenge, accepts valid construction
+- **`PasskeyAuthenticator::from_serialized_bytes()`**: empty bytes, wrong signature scheme flag, invalid BCS data
+- **Roundtrip serialization**: `to_bytes()` → `from_serialized_bytes()` produces identical authenticator
+- **Challenge parsing**: verifies challenge is correctly decoded from client_data_json
+
+### `src/crypto/move_authenticator.rs` — Construction & Serialization Tests
+
+Tests for MoveAuthenticator construction, address extraction, and serialization.
+
+- **`new_immutable()`**: creates correct `ImmutableOrOwned` input variant
+- **`new_shared()`**: creates `Shared` input with `mutable=false`, correct object_id and initial_shared_version
+- **`address()`**: extracts correct address from both immutable and shared variants via pattern matching
+- **Roundtrip serialization**: `to_bytes()` → `from_serialized_bytes()` for immutable, shared, and with call_args/type_args
+- **Error paths**: empty bytes, wrong flag, invalid BCS, unknown signature scheme flag
+
+### `src/crypto/multisig.rs` — Committee Validation Tests
+
+Tests for multisig committee `is_valid()` validation logic.
+
+- **Valid committees**: single member, multiple members, max 10 members, mixed key types, threshold less than total weight
+- **Invalid committees**: zero threshold, empty members, >10 members, zero-weight member, weight sum < threshold, duplicate members
+- **Aggregated signatures**: construction, bitmap access, signature collection
+
+### `src/object.rs` — Core Object Type Tests
+
+Tests for object reference types, owner variants, and object data.
+
+- **ObjectReference**: construction, `Hash`/`Eq` consistency, `Ord` ordering
+- **Owner**: all four variants, variant checks, `Ord` implementation
+- **ObjectData/ObjectType**: `Struct` and `Package` variants
+- **Object**: construction, field accessors
+- **GenesisObject/BalanceChange**: construction and field access
+
+### `src/events.rs` — Event Type Tests
+
+- **Event**: construction, field access, `Clone`/`Eq`
+- **TransactionEvents**: construction, data access
+- **BalanceChange**: positive/negative amounts, `Ord` ordering
+
+---
+
+## iota-sdk-transaction-builder
+
+### `src/builder/mod.rs` — Transaction Builder API Tests
+
+Tests for the `TransactionBuilder` covering transaction construction, gas configuration, and command generation.
+
+- **Gas configuration**: single/multiple gas objects, gas price, gas budget, gas sponsor
+- **Commands**: `transfer_objects`, `split_coins`, `merge_coins`, `move_call`, `publish`, `upgrade`, `make_move_vec`
+- **`send_coins`**: single coin with amount, multiple coins with merge (uses turbofish for type inference)
+- **Error cases**: missing gas objects, missing gas price, gas station without data
+
+### `src/types/move_arg.rs` — ULEB128 Encoding & Collection Serialization Tests
+
+Tests for the BCS serialization logic used in Move call arguments.
+
+- **`u32_as_uleb128()`**: zero, single-byte max (127), two-byte (128), multi-byte (300, 16384), max u32 (5-byte encoding)
+- **`MoveArgCollection` for `Option<T>`**: `None` encodes as `[0]`, `Some` encodes with `[1]` prefix
+- **`MoveArgCollection` for arrays**: length prefix + concatenated elements, empty array
+- **`MoveArgCollection` for `Vec<T>`**: length prefix + concatenated elements, empty vec
+- **`MoveArg` impls**: `PureBytes` identity, `&str` BCS encoding (ULEB128 length + UTF-8), `String`/`&String` match `&str`
+
+### `src/builder/gas_station.rs` — Version Parsing Tests
+
+- **`GasStationVersion`**: parsing valid versions, major/minor/patch accessors, comparison ordering
+- **Error handling**: invalid formats, non-numeric parts, leading zeros, extra parts
+
+### `src/unresolved.rs` — Unresolved Transaction Type Tests
+
+- **`UnresolvedTransaction`**: construction, sender, gas payment, expiration
+- **`UnresolvedGasPayment`**: default values, partial fields, objects, budget, price, owner
+- **`UnresolvedInputArgument`**: all variants, `is_mutable` for shared objects
+
+### `src/error.rs` — Error Variant Tests
+
+- **Display messages**: all 24 error variants
+- **Constructors**: `Error::client()`, `Error::signature()` wrapping
+- **From impls**: `base64ct::Error` conversion
+
+---
+
+## iota-sdk-graphql-client
+
+### `src/query_types/mod.rs` — BigInt Conversion Tests
+
+Tests for the `TryFrom<BigInt> for u64` conversion logic.
+
+- **Valid conversions**: positive integer, zero, `u64::MAX`
+- **Error cases**: overflow (`u64::MAX + 1`), negative value, non-numeric string, empty string
+
+### `src/pagination.rs` — Page Utility Tests
+
+Tests for pagination data structures and transformations.
+
+- **`Page::map()`**: transforms data while preserving page_info, empty page mapping
+- **`Page::is_empty()`**: true for empty, false for non-empty
+- **`Page::into_parts()`**: decomposes into (PageInfo, Vec<T>)
+- **`Page::new_empty()`**: default PageInfo values
+- **`Direction`**: default is `Forward`
+- **`PaginationFilter`**: default values
+
+### `src/error.rs` — Error System Tests
+
+- **Kind display**: all five variants
+- **Constructors**: `from_error`, `from_message`, `empty_response_error`, `graphql_error`
+- **From impls**: 9 error type conversions
+- **`std::error::Error` trait**: `source()` chain behavior
+
+### `src/faucet.rs` — Faucet Type Tests
+
+- **FaucetRequest**: JSON serialization/deserialization
+- **FaucetResponse**: successful/error response parsing
+- **CoinInfo**: construction and field access
+- **Edge cases**: empty coin lists, missing fields, null handling
+
+### `src/streams.rs` — Stream Utility Tests
+
+- **PageInfo**: construction, pagination state
+- **Stream behavior**: single page, empty pages
+- **Direction**: forward/backward pagination