update coverage for context.

[sassy]

Test coverage is not 100% in context.ts.
I add 2 case tests for context.

------------------|---------|----------|---------|---------|-------------------
File              | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
------------------|---------|----------|---------|---------|-------------------
All files         |   98.76 |    94.34 |     100 |   98.63 |
 client.ts        |     100 |      100 |     100 |     100 |
 context.ts       |   97.06 |    90.91 |     100 |   96.88 | 80,98
 index.ts         |     100 |      100 |     100 |     100 |
 speechBuilder.ts |     100 |      100 |     100 |     100 |
 verifier.ts      |     100 |      100 |     100 |     100 |
------------------|---------|----------|---------|---------|-------------------