Running Elixir Tests in Visual Studio Code/ElixirLS

keybindings.json

 {
    "key": "alt+t",
    "command": "workbench.action.tasks.runTask",
    "args": "mix test"
  }

tasks.json

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "mix test",
            "type": "shell",
            "command": "mix",
            "args": ["test", "--color", "--trace"],
            "options": {
                "cwd": "${workspaceRoot}",
                "requireFiles": [
                    "test/**/test_helper.exs",
                    "test/**/*_test.exs"
                ]
            },
            "problemMatcher": "$mixTestFailure"
        },
        {
          "label": "mix test file",
          "type": "shell",
          "command": "mix",
          "args": [
            "test",
            "${relativeFile}",
            "--color",
            "--trace"
          ],
          "options": {
            "cwd": "${workspaceRoot}",
            "requireFiles": [
              "test/**/test_helper.exs",
              "test/**/*_test.exs"
            ]
          },
          "problemMatcher": "$mixTestFailure"
        },
        {
            "label": "mix test focused",
            "type": "shell",
            "command": "mix",
            "args": [
                "test",
                "${relativeFile}:${lineNumber}",
                "--color",
                "--trace"
            ],
            "options": {
                "cwd": "${workspaceRoot}",
                "requireFiles": [
                    "test/**/test_helper.exs",
                    "test/**/*_test.exs"
                ]
            },
            "problemMatcher": "$mixTestFailure"
        },
    ]
}

To enable "rerun last task" command, you can add this to tasks:

"runOptions": {
  "reevaluateOnRerun": false
}