In #15178, we're switching hard-coded constants in tests to insta.

This issue targets updating datasource tests (datafusion/core/src/datasource).

Examples of tests that need to be switched to insta

• datafusion/datafusion/core/src/datasource/view.rs

  Lines 237 to 243 in 1eefd13

  	let expected = [
  	"+---------+---------+---------+",
  	"| column1 | column2 | column3 |",
  	"+---------+---------+---------+",
  	"| 1 | 2 | 3 |",
  	"| 4 | 5 | 6 |",
  	"+---------+---------+---------+",

• datafusion/datafusion/core/src/datasource/file_format/csv.rs

  Lines 935 to 938 in 1eefd13

  	"| sum(one_col.column_1) |",
  	"+-----------------------+",
  	"| 50 |",
  	"+-----------------------+"];

• datafusion/datafusion/core/src/datasource/view.rs

  Lines 548 to 551 in 1eefd13

  	Explain\
  	\n CreateView: Bare { table: \"xyz\" }\
  	\n Filter: abc.column2 = Int64(5)\
  	\n TableScan: abc projection=[column1, column2, column3]";

Check the original issue for tips on how to do the switch and examples of completed PRs.